Objectives Cognitive impairment is a common symptom of schizophrenia that has significant effects on quality of life and the activities of daily living. The present study examined the ability of transcranial direct current stimulation (tDCS) to improve cognitive function and clinical symptoms in patients with schizophrenia. Methods Fifty-six patients with schizophrenia were randomized to real-tDCS and sham-tDCS groups. The participants were stable for a period of 3months before study enrollment. Each group received 30min of active 2-mA tDCS or sham stimulation over the left dorsolateral prefrontal cortex (anode F3, cathode F4) once per day for 10 consecutive weekdays. The Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB) and Wisconsin Card Sorting Test (WCST) were used to evaluate cognitive function, and the Positive and Negative Syndrome Scale (PANSS), Clinical Global Impression-Schizophrenia scale (CGI-SCH), and Calgary Depression Scale for Schizophrenia (CDSS) were used to evaluate symptoms at baseline, after 10 sessions, and at 3-month follow-up. Results There was a significant time×group interaction, indicating that MCCB working memory (P=0.008) and overall scores (P=0.031) improved over time in the real-tDCS group compared to the sham-tDCS group. There was also a significant time×group interaction for depressive symptoms as evaluated by the CGI-SCH, which decreased over time in the real-tDCS group (P=0.041). tDCS treatment combined with antipsychotic medication was generally well-tolerated and safe. Conclusions Adjunct tDCS treatment is safe and effective for improving cognitive status in patients with schizophrenia.