Treatment options for binge eating disorder are limited in Japan. Thus, a small exploratory study was conducted to assess the efficacy of topiramate in Japanese patients with binge eating behavior. This was a prospective, open-label, single-arm, observational study conducted at a single hospital. Patients included in this study were outpatients. Topiramate was administered up to 14 months or until loss of follow-up. Initial dose of topiramate was 25 mg/day, and then the dose was gradually increased to optimal dose. The maximum allowed dose was 200 mg/day. The primary outcomes were the changes in the mean scores of Clinical Global Impression-Severity (CGI-S) scale for binge eating behavior from baseline, the frequency of binge eating and binge days per week. A total of 22 patients (4 males and 18 females) were included in this study. The mean duration of topiramate administration was 7.0 months. The mean score of CGI-S scale for binge eating behavior was significantly decreased from 3.68 ± 0.65 at baseline to 2.23 ± 1.02 (p < 0.001). Both frequency of binge eating and binge days per week were significantly decreased from 8.29 ± 8.07 times/ week at baseline to 1.95 ± 2.57 times/week (p = 0.002), and 4.80 ± 2.61 days/week to 1.98 ± 2.38 days/week (p = 0.001), respectively. The present study showed the potential of topiramate for the treatment of binge eating behavior. The efficacy and safety of topiramate in the treatment of binge eating disorder in the Japanese population should be confirmed in a large scale study.