Objectives A strong sense of belonging is crucial for the physical and mental health of older adults and their social interactions. The age-friendly city offers various opportunities for social participation of older adults. The present study aims to determine the role of age friendly-city indicators in predicting social belonging of older adults residing in Mohammadiyeh County, Qazvin Province, Iran. Methods & Materials This descriptive-analytical study was conducted on 300 older adults in 2022, who were selected by a cluster sampling method from six municipal districts of Mohammadiyeh County. Data were collected using a demographic checklist, an age-friendly city scale, and a social belonging scale. Data analysis was conducted in SPSS software version 23 using multivariate linear regression analysis. The significance level was set at 0.05. Results The mean age of participants was 67.55±6 years, ranging from 60 to 84 years. The majority of them were male (n=157, 52.33%), married (n=216, 72%), and illiterate (n=157, 52.33%). Among the age-friendly city indicators, the highest score was related to the safety/ease of transportation (16.86±4.51) and open public spaces (45.61±11.47) indicators. The results of multivariate regression analysis showed that marital status (β=-0.150, P=0.006), lower than high school education (β=0.170, P=0.003) and high school diploma (β=0.192, P=0.001), and the age-friendly city indicator of safety/ease of transportation (β=0.328, P<0.001) were predictors of social belonging in older adults. Conclusion The majority of older adults in Mohammadiyeh County are dissatisfied with age-friendly indicators. Those who feel safe and have easy access to public transportation are more likely to have a stronger sense of social belonging. The results of this study can effectively help policymakers and city managers in proper planning in order to develop an age-friendly city.