Objective: The authors investigated the relationship between the usefulness of CPT-11 + PLD combination therapy and the UGT1A1 genotype. Materials and Methods: Forty-one patients who provided informed consent were divided into the following two groups according to UGT1A1 genotypes: wild type and non-wild type. Adverse events, antitumor effect, and outcomes were compared between these two groups. Results: Twenty-three patients were wild type and 18 were non-wild type for UGT1A1. A total of 94 and 73 treatment cycles were prescribed to the wild-type and non-wild-type groups, respectively. No significant differences in the incidence of any grade 3 or higher adverse events were observed between the two groups. However, the next treatment cycle was postponed in 9.6% of the wildtype group and 12.3% of the non-wild-type group (p = 0.891). The antitumor effects as assessed by response rate were 26.1% in the wildtype group and 55.6% in the non-wild-type group (p = 0.054). The median observation period was 13 months. The median progression-free survival was three months in the wild-type group vs. five months in non-wild-type group (p = 0.913), while the median overall survival was 24 vs. 22 months (p = 0.535). Conclusions: This study did not demonstrate a statistically significant difference in the usefulness of CPT-11 + PLD combination therapy for recurrent ovarian cancer between the two groups of UGT1A1 genotypes. This study was considered to have significance as the first study conducted in Japan to prospectively evaluate the relationship between the usefulness of CPT-11-based chemotherapy and the UGT1A1 genotype for recurrent ovarian cancer.