Sustainability evaluation of irrigated and rain fed agro ecological system was taken up in Tamil Nadu, India. This study was conducted with the objective of measuring the sustainability with farm level indicators and Sustainable Rural Livelihood (SRL) framework, assessing the livelihood security of farmers and finally developing the optimum farm plans in both the agro ecological systems, Farm level indicators were developed by combining ecology, economy and society criteria. Ecological sustainability analyses showed that irrigated agro-ecological system is sustainable by having high soil fertility status and also by following integrated pest management. The irrigated agro ecological system is more economically viable than rain fed agro ecological system with higher output-input ratio, net... return and value addition. Higher input self sufficiency ratio, higher labour requirement to produce one physical unit of crop and higher food expenditure were observed in irrigated agro-ecological system. SRL framework analyses encompassed the evaluation of five capital assets of natural, financial, physical, capital and social. This analysis confirmed the earlier finding that irrigated agro-ecological system is more sustainable from farm level indicators approach. Livelihood security of farmers in both systems was analyzed with CARE model of Kenya and measured in terms of indices of food, economic, education, habitat and social network. It showed that farmers in irrigated agro ecological system were much secure especially from economic, habitat and social network purview. Finally development of sustainable farm plans through multi-objective goal programming was also attempted in the study, by satisfying economic, ecological and social goals. Finally policy implications were suggested to the Government for the development of irrigated farmers with suitable credit and extension policies and development of rain fed farmers with agricultural development and welfare programmes.