In the deregulated power system, the Independent System Operator (ISO) ensures the secure operating condition. The information about available Transfer Capability (ATC) is an index for system robustness and enables the operator to take decision on the proposed transactions. Hence ATC estimation plays a key role in secure operation of power system. A method is proposed to estimate ATC with less computation and an acceptable degree of accuracy through fuzzy logic. The proposed method is tested and validated on IEEE-14 bus system and compared with ac power flow based conventional method. © 2007 IEEE.