Objective: Investigate serum taurine level as a biomarker for early diagnosis and follow up of chronic myeloid leukemia, find correlation between serum taurine level in different phases of Chronic Myeloid Leukemia and number of blast cells in each phase, find correlation between serum taurine level and the percentage of BCR-ABL gene in body which is the diagnostic biomarker for chronic myeloid leukemia. Method: One Hundred and thirty eight chronic myeloid leukemia patients (male and female) were chosen from National Cancer Institute after their approval, patients classified into four groups (Chronic Phase (CP) of CML group, Accelerated Phase (AP) of CML group, Blast Phase (BP) of CML group& after Treatment group (Healing Patients from CML)) according to their Complete clinical examination, investigation and biochemical analysis. Thirty frank healthy control persons enrolled as volunteers. Complete clinical examination, investigation and biochemical analysis (liver and kidney functions, complete blood pictures, Cytology analysis), and the recent biomarker taurine, was measured for all patient and volunteers. Results: The data showed that, according to age, there were statistically significant difference between control group and after treatment group. We did not find a significant difference between gender in different groups (P=0.942).by comparing family history between groups we found that 62.5% of AP group had positive family history, 50% of BP group had positive family history, 44.3% of CP group had positive family history, 33.3% of controls had positive family history while no patients in after treatment group had positive family history .we found that median hemoglobin level were statistically significant differ between groups. By doing pairwise comparison we found that median HB level in AP group is differ from this in CP, after treatment and control group (P=0.027, 0.028, <0.001 respectively). In addition, this in control group is statistically differ from this in BP and CP groups (P=0.002 and <0.001 respectively). That median WBCS level were statistically significant differ between groups. By doing pairwise comparison we found that median WBCS level in after treatment group were differ from CP,AP groups(P=0.012,<0.001 respectively). Also control group differ from CP and AP groups (P=<0.001, <0.001 respectively) .we found that median ALT level were statistically significant differ between groups. By doing pairwise comparison we found that median ALT level in control group is differ from CP and AP (P=0.17, 0.21 respectively).also, median AST level were statistically significant differ between groups. By doing pairwise comparison we found that median AST level in control group is differ from CP and AP and after treatment groups (P=<0.001, <0.001 and 0.034 respectively). Bilirubin and urea were not statistically differ between groups. Creatinine were statistically significant differ between groups. By doing pairwise comparison we found that median creatinine level in control group is differ from AP, BP and CP group (P=<0.001, 0.034, <0.001 respectively). Alkaline phosphatase were statistically significant differ between groups. By doing pairwise comparison we found that median alkaline phosphatase level in control group is differ from AP and CP (P=0.008, <0.001).we found that median blast cells level were statistically significant differ between groups. By doing pairwise comparison we found that median blast cells level in CP group is differ from AP and BP(P=<0.001,<0.001 respectively). Median BCR-ABL level were statistically significant differ between groups. By doing pairwise comparison we found that median BCR-ABL level in CP group is differ from AP and BP (P=<0.001, <0.001 respectively). The most interesting thing that the Median serum taurine level were statistically significant differ between groups. By doing pairwise comparison we found that median taurine level in BP group is differ from CP and after treatment group(P=<0.001,<0.001 respectively) and in AP group is differ from CP, after treatment and control(P=<0.001,<0.001 respectively).we found that there is correlation between taurine level and different numeric variables , we found that age has fair negative correlation with taurine level meaning that for each year increase in age taurine level will decrease .also WBCS has good negative correlation with taurine level meaning that for each increase in in WBCS taurine level will decrease. In addition, RBCS and HB have good positive correlation with taurine level meaning that for each increase in RBCS or HB taurine level will increase. Platelets, neutrophils, bilirubin and urea show no significant correlation with taurine level. ALT and AST show week to fair negative correlation with taurine level. Creatinine has good negative correlation with taurine level. Number of Blast cells and BCR-ABL ratio show excellent negative correlation with taurine level meaning that when they increase taurine level decrease and vice versa . Conclusion: Serum taurine level is statistically significant differ between groups ,that decrease with the increase of the chronicity of disease and the number of blast cells , increase in normal frank control volunteers and after treatment patients which make it possible to be used as a pre biomarker for early diagnosis and follow up of chronic myeloid leukemia disease.