ABSTRACT Background Schizophrenia is a chronic degenerative brain disease. Cognitive impairment, the core symptom of this disease, affects the mood and social functioning of patients severely. Nonpharmacological therapies that both improve cognitive function and are suitable for patients with schizophrenia remain underdeveloped. Purpose This article was designed to explore the effects of group cognitive stimulation training (GCST) on cognitive function and social function in people with schizophrenia. Methods A randomized controlled trial was conducted. The 76 participants were allocated into either the experimental or control group using blocked randomization. The participants were all patients with chronic schizophrenia recruited from seven rehabilitation units in northern Taiwan who were 20–65 years old and scored 10–25 on the Montreal Cognitive Assessment Taiwan Version. The experimental group received the 60-minute GCST twice a week for 7 weeks, whereas the control group received standard treatment. All outcome indicators were analyzed at baseline and after intervention using generalized estimating equations. The primary outcome indicators included cognitive function assessed using the Taiwan version of the Montreal Cognitive Assessment, working memory assessed using the Wechsler Memory Scale–Third Edition, and executive function assessed using the Taiwanese version of the Frontal Assessment Battery. The secondary outcome indicator was social function assessed using the Social Function Scale–Taiwan short version. Results Generalized estimating equation modeling revealed the experimental group exhibited significant improvement in Montreal Cognitive Assessment total score (B = 1.33, SE = 0.65, p = .040) and Social Function Scale–Taiwan short version (B = 9.55, SE = 2.38, p < .001) after adjusting for nine covariates. No significant differences between the two groups in terms of working memory (B = 4.79, SE = 2.66, p = .071) or executive function (B = 0.53, SE = 0.63, p = .399) were found. Conclusions/Implications for Practice The results indicate that GCST positively impacts overall cognitive and social functions but not higher-order cognitive function (working memory and executive function). In clinical settings, GCST may be applied to improve cognitive function in people with schizophrenia. The findings of this study may inform the practice of mental health nurses to improve cognitive function in patients in clinical care.