Background: The latest National Comprehensive Cancer Network Guidelines for pancreatic adenocarcinoma recommended platinum-based chemotherapy for the patients with germline BRCA1/2 or PALB2 variants based on retrospective studies. However, the association between the efficacy of oxaliplatin-based chemotherapy and homologous recombination repair (HRR)-related gene variants has not yet been evaluated in a prospective study. Methods: This was a multicenter, prospective, observational study. Key inclusion criteria were: histologically confirmed pancreatic adenocarcinoma or adenosquamous carcinoma; candidates for systemic chemotherapy or currently under systemic chemotherapy for unresectable disease; age ≥ 20 years; Eastern Cooperative Oncology Group Performance Status 0–2; formalin-fixed paraffin-embedded cancer tissue available for genomic sequencing; and adequate hematological, liver, and renal function. Patients were assessed with the next generation sequencing (NGS)-based ACT-repair panel (ACT genomics; Taipei, Taiwan). ACT-repair panel is accredited by College of American Pathologists and is designed to detect short variants (SVs) including substitutions, insertions, deletions, and copy number variants of 35 genes including 8 HRR-related genes (ATM, ATR, BRCA1, BRCA2, PALB2, RAD51B, RAD51C, RAD51D). The primary endpoint was the one-year overall survival rate (1yr-OS%) after the initiation of oxaliplatin-based chemotherapy in patients who harbored pathogenic HRR gene variants. On the basis of published retrospective data, expected 1yr-OS% was set at ≥ 60% in this study. Results: Forty patients were enrolled from August 2018 to March 2020. Median age was 67 years (range, 49–81 years). Sequencing data were obtained from 39 patients (NGS success rate = 97.5%). Nine patients (22.5%) harboring HRR gene; ATM SVs (n = 4), BRCA2 loss of heterozygosity (LOH) (n = 3), BRCA2 SVs (n = 1), and PALB2 LOH (n = 1). Three patients received oxaliplatin-based chemotherapy as first-line chemotherapy, while the remaining six patients received it as second- or later-line oxaliplatin-based chemotherapy. The 1yr-OS% was 44.4%, and the median overall survival was 221 days (95% confidence interval, 79–NA days) after the initiation of oxaliplatin-based chemotherapy. In three patients who received oxaliplatin-based chemotherapy as first-line treatment, overall survivals were 703 (alive), 694 (alive), and 405 (dead) days, respectively. Conclusions: Efficacy of oxaliplatin-based chemotherapy on advanced pancreatic cancer harboring HRR-related gene variants did not meet the primary endpoint of 1yr-OS% (≥ 60%). Clinical trial information: UMIN000033655.