BACKGROUND: Ovarian cancer is the most aggressive gynecological tumor with high mortality. The ambivalent, both helper and suppressive effects of neutrophils on the cells of innate and adaptive immunity determines their important immunoregulatory role in the development of malignant tumors. AIM: Evaluation of the effect of serum interleukin-1β and circulating neutrophils CD16+ on progression-free time in advanced ovarian cancer. MATERIAL AND METHODS: In 42 primary patients with serous ovarian adenocarcinoma (median age 54 years) with ascites and 15 patients with benign ovarian tumors (median age 60 years) admitted for examination and treatment to the Regional Clinical Oncology Dispensary before receiving neoadjuvant antitumor treatment (2015–2020), the level of interleukin-1β in the blood serum was determined using enzyme immunoassay, and the number of CD16+ neutrophils was determined by fluorescence microscopy using monoclonal antibodies. Statistical processing was performed using Statistica 13 and Jamovi 2.4.14 programs. Progression-free time analysis of patients was performed using the Cox and Kaplan–Meier regression methods. RESULTS: It was found that the number of circulating CD16+ neutrophils in advanced ovarian cancer with ascites was lower than in benign ovarian tumors [48.0; 95% confidence interval (CI) 46.59–48.12 versus 50.0; 95% CI 48.51–49.76; p=0.017]. At the same time, the level of interleukin-1β in the blood serum in advanced ovarian cancer with ascites was higher than in benign ovarian tumors [2.52 (95% CI 2.50–3.37) versus 1.26 (95% CI 0.97–1.55) (p=0.0001)]. In multivariate Cox analysis in patients with ascites (odds ratio 4.334; 95% CI 1.83–10.23; p=0.001), both the CD16+ neutrophil count (odds ratio 0.73; 95% CI 0.62–0.86; p=0.0001) and serum interleukin-1β levels (odds ratio 1.90; 95% CI 1.41–2.57; p=0.0001) had prognostic significance for assessing progression-free time. CONCLUSION: The number of circulating CD16+ neutrophils and serum interleukin-1β levels simultaneously affect progression-free time in advanced ovarian cancer.