This paper presents a design automation method to optimize RFID tag antenna design with a genetic algorithm (GA) linked with an EM commercial simulation program MWS (Microwave Studio) manufactured by CST Co. The MWS simulator program is very well known program for antenna design. The GA is programmed with MATLAB and linked with MWS to get the results of RFID tag antenna simulation. The visual basic application (VBA) script language is used to link and execute between GA and MWS program. The test results getting from the MWS simulation program passed to the GA, and GA optimizes the design automatically.