This study aimed to investigate the short-term effectiveness of adalimumab therapy in patients with ulcerative colitis (UC), especially its rapid response.This retrospective, multicenter, cohort study involved 7 institutes in Japan, compiling data from patients with UC who had received at least 1 induction dose of 160 mg of adalimumab between June 2013 and May 2017. Patients should have a Lichtiger clinical activity index score of ≥5 at the initial adalimumab administration. Remission was defined as clinical activity index score of ≤4, whereas response was defined as a reduction of ≥50% from the baseline value. Rapid responders are defined as patients who achieved response at 2 weeks.A total of 91 patients were included in this study: 37.4% and 45.1% achieved clinical response at 2 and 8 weeks, respectively, whereas clinical remission rates 12 weeks were 45.1%. Among the rapid responders, 82.4% achieved clinical remission at 12 weeks. Multivariate logistic regression analysis identified a higher platelet count as an independent prognostic factor for a higher rate of rapid response. Receiver operating characteristic curve showed that a platelet counts cutoff value of ≥312 × 10/L was associated with a rapid response.Approximately 40% of patients with UC showed a rapid response to adalimumab therapy after 2 weeks. Up to 80% of the rapid responders also achieved remission at 12 weeks. A higher platelet count was identified as an independent prognostic factor for a higher rapid response rate.