Ansofaxine (LY03005) extended-release (ER) tablet is a potential triple reuptake inhibitor of serotonin, norepinephrine, and dopamine. This study assessed the efficacy, safety, and appropriate dosage of ansofaxine for the treatment of major depressive disorder (MDD).A multicenter, randomized, double-blind, placebo-controlled, dose-finding, Phase 2 clinical trial was conducted in China. Eligible patients with MDD (18-65 years) were randomly assigned to receive fixed-dose ansofaxine ER tablets (40, 80, 120, or 160 mg/day) or placebo for 6 weeks. The primary outcome measure was a change in the total score on the 17-item Hamilton Depression Rating Scale (HAMD17) from baseline to week 6.A total of 260 patients were recruited from October 2015 to September 2017. 255 patients received the study drug as the following: 40 mg (n = 52), 80 mg (n = 52), 120 mg (n = 51), and 160 mg (n = 51) ansofaxine and placebo (n = 49). Significant differences were found in mean changes in HAMD17 total scores at week 6 in the four ansofaxine groups vs. placebo (-12.46; χ  2 = -9.71, p = 0.0447). All doses of ansofaxine were generally well-tolerated. Treatment-related adverse events (TRAEs) occurred in 141 patients (303 cases), giving TRAEs incidence rates of 51.92%, 65.38%, 56.86%, and 62.75%in the 40, 80, 120, and 160 mg ansofaxine groups and 38.78% in the placebo group.Active doses (40, 80, 120, and 160 mg per day) of ansofaxine in a controlled setting were safe, tolerated, and effective in improving depression symptoms in MDD patients.© The Author(s) 2021. Published by Oxford University Press on behalf of CINP.