Objective: Patients treated with the antipsychotics experience significant weight gain with accompanying metabolic disorders. Although several clinical trials have assessed the effectiveness of pharmacologic interventions including metformin, aripiprazole, and topiramate in managing antipsychotic-induced weight gain, there is no satisfactory result so far. In addition, it is troubling to use centrally acting anti-obesity drugs because of their potential adverse effects on psychiatric diseases. The aim of this study was to investigate the efficacy of liraglutide 3.0mg on weight reduction among antipsychotic-treated obese patients. Methods: We retrospectively studied 16 obese patients with schizophrenia, schizoaffective disorder, or bipolar disorder who were treated with liraglutide 3.0 mg in Dongguk University Ilsan hospital. During first 3 months, changes in body weight were analyzed. The clinical global impression - severity scale (CGI-S) was used to rate the severity of psychiatric disorders. Dividing participants to responder (lost at least 5% of their body weight) or non-responder, we investigated the characteristics of responder. Results: Liraglutide 3.0 mg significantly decreased body weight (Estimated marginal means of body weight: week 0, 93.2 kg; week 1, 92.0 kg; week 4, 91.1 kg; week 8, 90.0 kg; week 12, 88.6 kg, p < 0.001). There were no significant differences for the CGI-S scores between baseline and week 12 (z score = -1.414, p = 0.157). Among 14 subjects who continued 12 weeks of treatment, 7 patients were a responder. Compared with non-responder, responder exhibited lower waist circumference (97.4 ± 12.0 vs. 115.1 ± 11.1, p = 0.039) and triglyceride level (168.4 ± 70.0 vs. 257.1 ± 75.3, p = 0.041). Nausea was the most common adverse events with liraglutide 3.0 mg (5 of 16 [31.3%]). Conclusion: 3.0 mg of liraglutide decreased body significantly in antipsychotic-treated obese patients without altering the status of psychologic diseases. Patients with modest degree of metabolic derangement might have a better response to liraglutide. A randomized controlled study is required for confirmation.