Background Although patients with advanced gastric cancer (AGC) have a poor prognosis when conventional therapies fail, they are often candidates for phase I trials. However, there is no detailed report on clinical outcomes of patients with AGC treated in phase I trials. Methods We retrospectively reviewed the medical records of 66 consecutive patients with AGC enrolled in phase I trials between March 2008 and July 2014 at our institution in Japan. Results Median age was 66 years (range, 28-78 years) and median number of previous lines of conventional chemotherapy was 3 (range, 1-6). Five (8.6 %) and seven (12 %) patients showed objective response and stable disease > 3 months, respectively. Although the time to treatment failure (TTF) of the best phase I treatment was shorter than that of the last line of conventional chemotherapy (median 1.5 vs. 2.3 months; P = 0.002), TTF of the best phase I treatment was longer than that of the last line of treatment in 21 patients (32 %). Severe adverse events and grade 3 or higher toxicities were reported in eight (12 %) and 13 patients (20 %), respectively. No treatment-related death was observed. Median survival time from the start of phase I treatment was 7.5 months, and four deaths (6 %) within 30 days after last administration were observed. Conclusion Phase I trials of patients with AGC was acceptably feasible with some efficacy signal. Our results suggest that phase I trials might be one treatment option for patients with AGC when conventional therapies fail.