Previous research has identified loneliness as a significant social stressor among the older adult population, and highlights the scarcity of empirical research on the efficacy of group play therapy as a method for addressing loneliness in this demographic. This study aimed to explore the impact of group play therapy on reducing feelings of loneliness among older individuals. A randomized clinical trial was carried out in 2018 on 60 older adult participants from two governmental health centers in Mashhad, Iran. The intervention group received adult-centered play therapy for 12 sessions over 6 weeks, with each session lasting 60 min. The therapy protocol combined traditional and modern games, structured into three stages: warm-up, working and closing. The University of California, Los Angeles (UCLA) scale was used to measure feelings of loneliness at baseline and after the intervention. Data analysis was carried out using SPSS version 21. There was a significant decrease in feelings of loneliness in the intervention group compared with the control group (P < 0.001). Additionally, a significant difference in feelings of loneliness was observed within the intervention group between baseline and follow up (P < 0.001). Group play therapy, involving a combination of traditional and modern games, can reduce feelings of loneliness among older adults. This method can promote healthy aging and improve mental health issues, such as loneliness, among older people. These findings can be utilized in healthcare centers and nursing homes for older adults. Geriatr Gerontol Int 2024; 24: 1067-1076.