Aim: To investigate the relationship between tumor volume and serum microsomal prostaglandin E2 (mPGE2) levels in patients with astrocytic tumors., Material and Methods: The study included patients with astrocytic tumors who were treated at our clinic between August 2015 and December 2016. Preoperative and postoperative contrast-enhanced cranial magnetic resonance imaging (MRI) scans were performed (within the first 24 h), and preoperative and postoperative residual tumor volumes were calculated. Microsomal prostaglandin E2 (mPGE2) levels were measured and compared in the serum samples of the patients before surgery, on the first day after surgery, and at 1 week after the surgery., Results: The study included 20 patients, 13 of whom were males and 7 were females, with a mean age of 57.20 ± 14.66 yr. The mean postoperative tumor volume was 9,180.69 mm3 (range, 0.00-41,961.60), which was significantly lower than the preoperative mean tumor volume of 37,323.84 mm3 (range, 4,457.40-108,247.20; z = -3.920, p < 0.001). On the first postoperative day, the mean mPGE2 level was 1,776.50 pg/ml (range, 771-5,010), which was similar to the preoperative mean mPGE2 level of 1,769.20 pg/ml (range, 681-3,480). On the seventh postoperative day, the mean mPGE2 level was 955.50 pg/ml (range, 31-2,130), which was significantly lower than the preoperative and postoperative first-day mean mPGE2 levels (p < 0.001). No correlation was found between preoperative and postoperative tumor volumes and mPGE2 levels., Conclusion: Compared with preoperative mPGE2 levels, mPGE2 levels decreased significantly on the seventh postoperative day. However, no correlation was observed between the tumor volume removed and decrease in mPGE2 levels.