IN THIS PAPER, A NEW NUMERICAL METHOD FOR SOLVING partial INTEGRO-differential equations (PIDES) BASED ON AN OPTIMAL CONTROL TECHNIQUE IS PROPOSED. IN THIS METHOD, First THE GIVEN EQUATION IS TRANSFORMED TO AN OPTIMAL CONTROL PROBLEM USUALLY KNOWN AS CONJUGATE PROBLEM. THEN, CONTROL AND STATE VARIABLES ARE APPROXIMATED BY THEIR CHEBYCHEV EXPANSIONS AND THE OBTAINED CONJUGATE PROBLEM IS REDUCED TO AN OPTIMIZATION PROBLEM SUBJECT TO EQUALITY ALGEBRIC CONSTRAINTS. FINALLY, BY USING A PROPER NUMERICAL OPTIMIZATION TECHNIQUE, THE CHEBYCHEV COEFFICIENTS ARE CALCULATED AND THE APPROXIMATE SOLUTION OF THE INITIAL PROBLEM IS ACHIEVED. A NUMERICAL EXAMPLE IS PRESENTED TO ILLUSTRATE THE PERFORMANCE AND ACCURACY OF THE PROPOSED METHOD.