In some countries, including Indonesia, labelling of GMO products is mandatory for giving consumers the right to choosebetween GMOs and conventional products. Therefore, development of methodology that can detect a specific geneticallymodified (GM) crops and to verify the absence or presence of GM material in a product including raw materials (e.g. grains)and/or their derivatives is needed. The objectives of this study were to find the most efficient screening methods to detectwhether or not a product is GM material and to develop a specific detection method to identify GM product BT11 and GA21. Inaddition, present study was also aimed to obtain a duplex detection method for both GM products. Two GM-maize, including theBT11 and GA21 lines of maize (Zea mays L.), and one plant, namely NK11 as the nontransgenic control, were used as plantgenetic materials in the event-specific detection of maize. The target gene from each sample was amplified in different reaction(simplex) using both the event specific primer and the endogenous maize reference, Zein, as internal control. Furthermore, induplex PCR, two targets were simultaneously amplified in the same reaction. The results showed that detection method of theGM product obtained from present study enabled us to screen the GM products and specifically the event of BT11 and GA21using simplex and duplex methods. The duplex method is more efficient because it can detect two GM crops in one timecompared to simplex method that only can detect GM crop one by one.