Because mFOLFOX6 has few contraindications, it is useful for poor performance status(PS)cases. However, in Japan, there are some reports that the dose is reduced easily. We retrospectively examined the safety/usefulness of the full dose mFOLFOX6(first-line)for advanced colon cancer patients with poor PS. Four of five cases had improved PS. The response rate was 60%. Grade 3/4 adverse events were infection, leukopenia, and neutropenia. Treatment-related deaths within 60 days of starting treatment were absent. Full-dose mFOLFOX6 for poor PS may be beneficial. However, we must consider the increased risk of adverse events.