Purpose: Capecitabine plus oxaliplatin (CAPOX) is one of the standard first-line treatments for unresectable, advanced, or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma. Camrelizumab shows promising antitumor activity in advanced or metastatic G/GEJ adenocarcinoma in a phase I study. We reported the outcomes of cohort 1 in a multicenter, open-label, phase II trial, which assessed camrelizumab in combination with CAPOX followed by camrelizumab plus apatinib as a first-line combination regimen for advanced or metastatic G/GEJ adenocarcinoma. Patients and Methods: Systemic treatment-naive patients with EGFR2-negative advanced or metastatic G/GEJ adenocarcinoma received initial camrelizumab plus CAPOX for 4-6 cycles, and patients without progressive disease were administrated subsequent camrelizumab plus apatinib. Primary endpoint was objective response rate (ORR). Results: All 48 enrolled patients comprised the efficacy and safety analysis population. The ORR was 58.3% [95% confidence interval (CI), 43.2-72.4] with this combination regimen. Median duration of response was 5.7 months (95% CI, 4.4-8.3). Median overall survival was 14.9 months (95% CI, 13.0-18.6), and median progression-free survival was 6.8 months (95% CI, 5.6-9.5), respectively. The most common grade >= 3 treatment-related adverse events (>10%) were decreased platelet count (20.8%), decreased neutrophil count (18.8%), and hypertension (14.6%). Treatment-related death occurred in 1 patient (2.1%) due to abnormal hepatic function and interstitial lung disease. Conclusions: Camrelizumab combined with CAPOX followed by camrelizumab plus apatinib demonstrated encouraging antitumor activity and manageable toxicity as firstline therapy for patients with advanced or metastatic G/GEJ adenocarcinoma.