e17539 Background: This study analyzes the levels of VEGF1 in ascites and serum before and after intraperitoneal infusion of bevacizumab, aiming to explore the optimal administration route for treating recurrent ovarian cancer accompanied by ascites. Methods: Sixty-seven patients with advanced recurrent ovarian cancer and significant ascites were treated with intraperitoneal infusion of bevacizumab combined with chemotherapy. Under ultrasound guidance, a peritoneal drainage tube was placed, and the volume of ascites was measured before the infusion. The effects of the treatment were assessed by measuring the ascites volume during the 2nd to 3rd treatment (final ascites drainage) and by analyzing and comparing the levels of Vascular Endothelial Growth Factor 1 (VEGF1) in both ascites and serum. Results: The average volumes of ascites before and after treatment were 4229.97 ml and 5.42 ml, respectively (P<0.0001), with an overall response rate (ORR) of 89.6% (60/67). Before and after treatment, the levels of VEGF1 in ascites were 283.86 pg/mL and 18.76 pg/mL, respectively (P<0.0001). Before and after treatment, serum levels of VEGF1 were 80.67 pg/mL and 61.25 pg/mL, respectively (P<0.0001). Before treatment, the level of VEGF1 in ascites at 283.86 pg/mL was significantly higher than in serum, which was 80.67 pg/mL (P<0.0001). The reduction in VEGF1 levels following intraperitoneal infusion was over tenfold greater in serum compared to ascites. When the cutoff value for VEGF1 in ascites was set at 37.12 pg/mL, the sensitivity was 80.28%, and the specificity was 91.55%. Conclusions: The combined treatment of intraperitoneal infusion of bevacizumab with chemotherapy is an effective strategy for controlling ascites in recurrent ovarian cancer. Keywords: Bevacizumab, Intraperitoneal Infusion, Recurrent Ovarian Cancer, Ascites, Vascular Endothelial Growth Factor 1 (VEGF1).