Background and Aim To evaluate the onset of symptomatic response with vedolizumab in patients with moderate-to-severe ulcerative colitis in Japan. Methods Patients were randomized to receive vedolizumab 300 mg or placebo at Weeks 0, 2, and 6. Mayo subscores were analyzed in patients with baseline stool frequency (SF) ≥1 and rectal bleeding (RB) ≥1. In patients with baseline SF ≥2 and RB ≥1, the proportion who achieved SF ≤1 and RB = 0 was determined. Results Patients were randomized to vedolizumab ( n = 164) or placebo ( n = 82). Decrease from baseline in mean SF subscore was greater with vedolizumab versus placebo from Week 2 (−6.6%; 95% confidence interval [CI], −16.2, 3.0), with a greater difference in anti-tumor necrosis factor (TNF)α-naive patients (vedolizumab vs. placebo, −13.2%; 95% CI, −29.7, 3.3). Mean percentage decrease from baseline RB subscore was numerically greater with vedolizumab versus placebo from Week 6 in anti-TNFα-naive patients (−10.7%; 95% CI, −33.0, 11.5). More patients in the anti-TNFα-naive subgroup achieved SF ≤1 and RB = 0 with vedolizumab versus placebo at Week 2 (14.8%; 95% CI, 2.5, 27.0) and Week 6 (20.3%; 95% CI, 4.4, 36.2). Patients with SF ≤1 and RB = 0 at Week 2 had higher clinical response, clinical remission, and mucosal healing rates at Week 10 than those without. Conclusions Our results indicate that vedolizumab induces a rapid symptomatic response, particularly in anti-TNFα-naive patients, and suggest that early symptomatic improvement predicts treatment response at Week 10 (NCT02039505).