Transcranial direct current stimulation (tDCS) can be an effective treatment for depression, however, the duration of the stimulation session, among other parameters, needs to be optimized. 69 mild to moderately depressed patients (age 37.6±10.5years, 19 men) were randomized into three groups – 30-, 20-minute or sham tDCS. 10 daily sessions of anodal/sham tDCS of the left DLPFC (0.5mA; electrode 3,5×7cm) combined with 50mg/day of sertraline were performed. Mood, cognition and BDNF level were assessed before and after the treatment. A significant difference between groups was observed in the percent change of the Hamilton Depression Rating Scale (F(2, 66)=10.1; p<0.001). Sham group (43.4%±18.1) had a smaller improvement compared to the 30-minute (63.8%±13.4; 95% CI: 11.23–29.44; p=0.00003) and 20-minute group (53.2%±15.3; 95% CI: 0.21–19.26; p=0.045). 30-minute group had significantly greater percent improvement than 20-minute group (95% CI: 1.74–19.46; p=0.02). Responders constituted 89%, 68%, and 50% and remitters – 70%, 27%, and 35% in the 30-, 20-minute and sham groups, respectively. A significant difference in the number of responders was observed between 30-minute vs. sham group (odds ratio=8; 95% CI, 2.59–24.69; p=0.001), in remission rate – between 30-minute vs. sham (odds ratio=4.40; 95% CI, 2.02–9.57; p=0.02) and vs. 20-minute (odds ratio=6.33; 95% CI, 2.85–14.10; p=0.003) groups. Two hypomania cases and one case of blood pressure elevation were detected in the 20-minute group. Among neuropsychological tests, only the change in Digit Span Backwards test showed a significant interaction between groups (TIME*GROUP; F(2, 65)=6,6, p=0.002); a greater improvement was observed in both active groups compared to sham (p<0.05). The change in BDNF level after the treatment did not show the significant difference between groups. tDCS of 20- or 30-minutes combined with sertraline are efficient for the treatment of mild and moderate depression; the effect of 30min stimulation exceeds the one obtained from 20min. •69 depressed patients were randomized into three groups: 30-, 20-minute or sham tDCS.•10 daily sessions of tDCS of the DLPFC combined with 50mg sertraline were performed.•Significant augmenting effect of active tDCS on sertraline treatment was shown.•Effect of tDCS during 30min exceeds one obtained during 20min.•2 hypomania cases and 1 case of blood pressure elevation were detected.