Background & Aims: Immune thrombocytopenia is a disorder characterized by decreased platelet production and degradation. The objectives of our study were to assess the relationship between 1,25(OH)2D3 levels and ITP based on sex, age, and duration of disease. Materials & Methods:The present study was retrospectively conducted by reviewing medical records of the ITP patients. Demographic data including age, sex, disease history and serum vitamin D levels were performed and collected in a pre-designed form. Data were reported as Mean ±SD and as frequency (percentage). Independent t-test or ANOVA tests were used to compare the mean serum levels of vitamin D in terms of sex, age or disease history.Results: A total of 140 subjects (71 females and 69 males) with mean age± SD of 39.90 ± 16.11 years enrolled in the study. The mean serum vitamin D level in patients was 18.85 ± 10.87. There was no significant relationship between sex and serum vitamin D level (P=0.943). Patients in the range of 30-40 years have the most frequency and the lowest level of vitamin D in serum (17.11± 9.68 ng/ml).There was no association between age and vitamin D based on Pearson's test (p=0.181). Vitamin D level in acute ITP patients was lower than chronic ITP patients, but this difference was not meaningful (p=0.403). Conclusion:According to the findings of this study vitamin D can be administered as a new immunomodulatory therapy in patients with ITP.