The concept of group formation and collectivization by organizing at the regional level is very important in the era of globalization and free trade liberalization. FPOs organize small farmers for forward linkages such as collective, marketing, processing, and market-driven agriculture production, as well as backward linkages for inputs like seeds, fertilizers, credit, insurance, knowledge, and extension services. Even though FPOs are doing well, still they face lot of challenges and struggle for their sustainability. Keeping these factors in view, the current study was done to determine the constraints, that Farmers' Producers Organization (FPO) faced for sustainable functioning. The study was conducted in Pennagaram block of Dharmapuri district in Tamil Nadu. 100 members of FPO were selected for the study. The interview schedule is used to collect the data. Rank Based Quotient (RBQ) was used to analyse the data collected. The results showed that lack of initiatives among the FPO members with the RBQ score of 83.83 under personal constraints, lack of well-developed processing facilities with the RBQ score of 90.00 under infrastructural constraints, lack of crop insurance facilities with the RBQ score of 93.00 under economic constraints, high transportation cost with the RBQ score of 95.17 under marketing constraints, weak economic status to run the organisation with the RBQ score of 86.38 under organisational constraints and lack of timely, cheap and good quality inputs with the RBQ score of 94.00 under technical constraints were the major constraints faced by the FPO members. Initiation among the FPO members, well developed processing and marketing facilities in their villages, provision of crop insurance for affected farmers, tax exemption, inclusion of their millets production in ration shops for supply are the suggestions expressed by the FPOs for their sustainability.