The aim of this study was to evaluate the efficacy and safety of modified docetaxel, oxaliplatin, capecitabine (DOC) combination chemotherapy, followed by maintenance capecitabine as first-line therapy for patients with metastatic gastric or gastroesophageal junction (GEJ) cancer. Treatment consisted of docetaxel 35 mg/m2 (days 1–8), l-OHP 85 mg/m2 (day 1), and capecitabine 750 mg/m2 twice daily (days 1–14), every 3 weeks. After six cycles of DOC, patients who did not progress received maintenance treatment with three-weekly capecitabine 1000 mg/m2 twice daily (days 1–14), until disease progression or unacceptable toxicity. Six-month disease control rate (DCR) was the primary endpoint and overall survival (OS), progression-free survival (PFS) and safety were the secondary endpoints. The Kaplan–Meier method was applied to estimate OS and PFS. Between July 2014 and September 2017, 37 patients with metastatic gastric or GEJ cancer were enrolled at our institution. Upon completion of the DOC regimen, 35 patients (94.5%) received capecitabine as maintenance chemotherapy for a median of 7 cycles (range, 3–14 cycles). The six-month DCR was 83.7% [95% confidence interval (CI), 71.8–95.6%], median PFS was 8.2 months (95% CI, 6.3–9.8 months), and median OS was 14.4 months (95% CI, 11.7–18.6 months). During DOC chemotherapy, the most common grade 3–4 adverse events were neutropenia (29.7%), anemia (10.8%), and diarrhea (10.8%). During maintenance treatment, toxicity was sporadic and mainly of grade 1–2. Modified DOC followed by capecitabine as maintenance chemotherapy seems to be an active and well tolerated first-line treatment strategy for patients with metastatic gastric and GEJ cancer.