This multicenter, randomized phase III trial evaluated the efficacy and safety of perioperative camrelizumab (an anti-PD-1 antibody) plus low-dose rivoceranib (a VEGFR-2 inhibitor) and S-1 and oxaliplatin (SOX) (SOXRC), high-dose rivoceranib plus SOX (SOXR), and SOX alone (SOX) for locally advanced gastric or gastroesophageal junction (G/GEJ) adenocarcinoma.Patients with T3-4aN + M0 G/GEJ adenocarcinoma were randomly assigned (1:1:1) to receive perioperative treatment with SOXRC, SOXR, or SOX. The primary end points were pathologic complete response (pCR) and event-free survival. The Independent Data Monitoring Committee recommended stopping enrollment in the SOXR group on the basis of the safety data of the first 103 randomly assigned patients in the three groups. The patients were then randomly assigned 1:1 to the SOXRC or SOX groups. This report presents the pCR results obtained per protocol for the first 360 randomly assigned patients who had the opportunity for surgery in the SOXRC and SOX groups.In the SOXRC and SOX groups, of the 180 patients in each group, 99% and 98% of patients received neoadjuvant therapy, 91% and 94% completed planned neoadjuvant therapy, and 86% and 87% underwent surgery, respectively. The pCR was significantly higher in the SOXRC group at 18.3% (95% CI, 13.0 to 24.8) compared with 5.0% (95% CI, 2.3 to 9.3) in the SOX group (difference of 13.7%; 95% CI, 7.2 to 20.1; odds ratio of 4.5 [95% CI, 2.1 to 9.9]). The one-sided P value was <.0001, crossing the prespecified statistical significance threshold of P = .005. Surgical complications and grade ≥3 neoadjuvant treatment-related adverse events were 27% versus 33% and 34% versus 17% for SOXRC and SOX, respectively.The SOXRC regimen significantly improved pCR compared with SOX alone in patients with G/GEJ adenocarcinoma with a tolerable safety profile.