We evaluate the efficacy and toxicities of low-dose FP therapy in the treatment of advanced and recurrent gastric and colorectal adenocarcinomas. 104 patients (gastric adenocarcinoma: 52, colorectal adenocarcinoma: 52) were enrolled. Low-dose FP therapy consisted of 5-FU (160 mg/m2/day every day by continuous infusion) and cisplatin (3 mg/m2/day in 100 ml of normal saline by infusion over 30 minutes on days 1-5/W). Patients were treated for 4 consecutive weeks with subsequent one-week rest period. Ninety-four of 104 patients completed this therapy, and the treatment accomplishment rate was 90%; 82% in gastric adenocarcinomas, 96% in colorectal adenocarcinomas. Two cases had CR, and 47 cases had PR, with an overall response rate of 52.1%. Response rates, 50% survival time, 1-year survival rates, and 2-year survival rates were 65.9%, 249 days, 33.7%, 19.7% in gastric adenocarcinomas, and 40.0%, 466 days, 56.7%, 29.4% in colorectal adenocarcinomas, respectively. Nausea/vomiting was the most common toxicity, occurring in 44.2% of patients treated and was predominantly mild to moderate (up to Grade 2). In 5 cases Grade 3 toxicity was observed. Low-dose FP therapy has a high antineoplastic effect and low-grade toxicity, and this therapy should become the first-choice chemotherapy for the treatment of advanced and recurrent gastric and colorectal adenocarcinomas.