This study aimed to estimate the medical costs among patients with ovarian cancer across distinct phases of care and surgical years. This population-based retrospective cohort study identified newly diagnosed ovarian cancer patients who underwent surgery based on nationwide claims data from Korea (2012-2019). Medical costs were categorized into 5 phases: neoadjuvant chemotherapy, surgery, frontline chemotherapy, monitoring, and recurrence. Total and cancer-related costs were analyzed by surgical year on a per patient and per patient per month (PPPM) basis. Per patient costs were estimated for each phase, with up to one year of follow-up per phase, for patients identified between 2013 and 2016. Generalized linear models (GLMs) examined associations between surgical year and cancer-related costs. Among 10,594 patients, median cancer-related costs per patient were highest in the recurrent phase ($20,548), followed by the frontline chemotherapy ($7,005), neoadjuvant chemotherapy ($5,870), surgery ($4,965), and monitoring phases ($1,906). The median surgery phase costs per patient increased from $4,254 in 2013 to $5,676 in 2016; recurrent phase costs increased from $17,289 to $26,750. GLM analysis revealed that per patient and PPPM costs significantly increased over time, particularly in the surgery and recurrent phases. Compared with the cost per patient in 2013, the cost per patient in 2016 was 27% higher for the surgery phase and 49% higher for the recurrent phase. Ovarian cancer-related costs have significantly increased over time, especially in the surgery and recurrent phases, thus highlighting the growing economic burden and the need for cost-effective care strategies.