Purpose: This study aims to specify the effects of Cognitive Stimulation Therapy based on Roy's adaptation model (RAM) on Alzheimer's patients’ coping and adaptation skills, cognitive functions, and quality of life (QOL). Design and methods: This is an experimental and randomized controlled trial. Patients in the experimental group received cognitive stimulation therapy (CST) based on RAM. Findings: The cognitive function level of the experimental group was found to be higher than that of the control group at the end of the measurements (performed in the 7th week); the difference was found to be statistically significant (P <.05). In the experimental group, dimensions of troubleshooting and focusing, making physical decisions, attention processing, systematizing, learning, and establishing relationships were found to be better than those of the control group after the application, and the difference was found to be statistically significant (P <.05). However, after the application, QOL of the experimental group was found to be better than that of the control group following the measurements; the difference was found to be statistically significant (P <.05). Practice implications: Psychiatric nurses should evaluate the patients using Standardize Mini-Mental Test Examination before applying RAM-based CST, and they should apply CST to early- and mid-stage Alzheimer's disease (AD) patients at the end of the evaluation and work with groups consisting of six persons at most. Since the cognitive functions of individuals with AD decline from the first stage, coping-adaptation, and QOL levels will also be affected, so it is recommended to evaluate the cognitive functions, coping-adjustment and QOL levels of individuals before applying RAM-based CST. Trial registration number: NCT02229474.