Background: Bilastine, a novel non-sedating second-generation H1-antihistamine, has been widely used in the treatment of allergic rhinoconjunctivitis and urticaria with a recommended dose of 20 mg once daily in most European countries since 2010. We evaluated its efficacy and safety in Japanese patients with chronic spontaneous urticaria (CSU). Methods: We conducted a multicenter, randomized, double-blind, placebo-controlled phase II/III study (trial registration No. JapicCTI-142574). Patients (age, 18–74 years) were randomly assigned to receive bilastine 20 mg, 10 mg or placebo once daily for 2 weeks. The primary efficacy endpoint was the change from baseline (Day −3 to 0) in total symptom score (TSS) at 2 weeks (Day 8–14), consisting of the itch and rash scores. Results: A total of 304 patients were randomly allocated to bilastine 20 mg (101 patients), bilastine 10 mg (100 patients), and placebo (103 patients). The changes in TSS at 2 weeks were significantly decreased by bilastine 20 mg than did placebo (p < 0.001), demonstrating the superiority of bilastine 20 mg. Bilastine 10 mg also showed a significant difference from placebo (p < 0.001). The TSS changes for the bilastine showed significant improvement from Day 1, and were maintained during the treatment period. The Dermatology Life Quality Index scores were also improved in bilastine than in placebo. The bilastine treatments were safe and well tolerated. Conclusions: Two-week treatment with bilastine (20 or 10 mg) once daily was effective and tolerable in Japanese patients with CSU, demonstrating an early onset of action.