Objective:To evaluate the role of lysophosphatidic acid (LPA) as a tumor marker in diagnosis and follow-up of patients with epithelial ovarian cancer. Methods: Eighty-seven epithelial ovarian cancer patients, 74 benign ovarian tumor patients, and 50 healthy women were enrolled in the study. Twenty-nine of 87 epithelial ovarian cancer patients were followed up for 6 cycles of paclitaxel-carboplatin chemotherapy. CA-125 and total plasma LPA levels were measured preoperatively and before each chemotherapy cycle. Results: Preoperative total plasma LPA and serum CA-125 levels were significantly higher in patients with epithelial ovarian cancer compared to patients with benign ovarian tumors and healthy women. Cut-off value for LPA was determined as 1.3 μmol/L and sensitivity, specificity, positive predictive value and negative predictive value were 95%, 92%, 95% and 92%, respectively. Mean total plasma LPA level of 29 patients who received chemotherapy was 7.21±6.63 μmol/L preoperatively and 6.84±6.34 μmol/L, 6.34±5.92 μmol/L, 6.14±5.79 μmol/L, 5.86±5.68 μmol/L, 5.23±5.11 μmol/L and 5.21±5.32 μmol/L in measurements held just before the 1st, 2nd, 3rd, 4th, 5th and 6th chemotherapy cycles, respectively (ANOVA, p=0.832). Total plasma LPA levels decreased slightly with chemotherapy administration and there was a weak negative correlation (Spearman, rs=−0.151, p=0.034), compared to a significant negative correlation in CA-125 (Spearman, rs=−0.596, p＜0.001). Conclusion: LPA is a better biomarker for diagnosis of epithelial ovarian cancer compared to CA-125. However, measurement of total plasma LPA levels during chemotherapy administration have no superiority to the serum CA-125 levels.