According to their location and characteristics, peri-urban areas are increasingly exposed to extensive changes because of the expansion of cities in various dimensions. In these areas, due to the reduction of rural agricultural lands, land-use change, fragmentation of agricultural lands, and increasing urban population, one of the issues that need more attention in these areas is food security as the agenda 2030 Sustainable Development Goals. Accordingly, this article has identified the factors affecting livelihood diversification regarding sustainable food security in peri-urban areas of Iran. After accurately identifying these factors, it also examines the effectiveness of livelihood diversification to sustainable food security in environmental-ecological, socio-economic, political-cultural, and infrastructural dimensions. This research has been done by the descriptive-analytical method in the peri-urban of Tehran. Inferential statistics, correlation relationships, stepwise linear regression, and a multiple-choice logit model were used to analyze the data. Findings showed that the influential factors in livelihood diversity in peri-urban areas of Tehran are training and awareness, knowledge and skills, institutionalism, access to resources, partnership for investment, and marketing of products. Diversification within agricultural sector activities such as agriculture, horticulture, livestock, and aquaculture significantly impact sustainable food security. Diversification within non-agricultural activities such as support services and agricultural production has the most negligible impact on the dimensions of sustainable food security. Among the variables included in the regression equation, the rest remain in the equation except for the variables of diversification in non-agricultural activities such as conversion and complementary industries and handicrafts and workshops in the village. Thus, diversification of activities has a positive effect on improving sustainable food security.