Uterine serous carcinoma (USC) is a rare but aggressive subtype of endometrial cancer lacking efficacious treatments. USC bears molecular and pathological resemblance to high-grade serous ovarian cancer, for which mutations in homologous recombination repair (HRR) genes have been associated with better treatment outcomes with platinum-based chemotherapy and poly-ADP ribose polymerase 1/2 inhibitors (PARPi). We aimed to investigate the prevalence of tumor HRR (tHRR) gene mutations and its potential prognostic value in USC patients. Sixty consecutive USC patients with available tumor tissue samples and complete follow-up records were included. Tumor mutations in relevant HRR genes were identified using next-generation sequencing and correlated with the progress-free survival (PFS) and disease-specific survival (DSS) of the patients. Among the 60 patients’ USC, 22 (36.7%) carried tumor HRR gene mutations (tHRRmt), with ATM, BRCA1, and BRCA2 being the most frequently mutated genes. Survival analysis showed similar PFS (HR, 0.500; 95% CI, 0.203–1.232; p = 0.132), but significantly longer DSS in the tHRRmt patients than in the HRR gene wild-type (tHRRwt) patients (HR, 0.176; 95% CI, 0.050–0.626; p = 0.007). In FIGO stage III and IV patients, the tHRRmt group also displayed longer DSS than the tHRRwt group (p = 0.008). Notably, USC patients with abnormal p53 in our cohort, both PFS and DSS were significantly longer in the tHRRmt group over the tHRRwt group (p = 0.040 and p = 0.008, respectively). The HRR gene mutations are highly prevalent in USC and may be related to better clinical outcomes as a prognostic marker. Further study is needed to confirm whether tHRRmt patients may benefit from treatments targeting homologous recombination such as platinum and PARPi.