This study was aimed to develop a novel qualitative multiplex polymerase chain reaction (PCR) for simultaneous detection of genetically modified (GM) soy and maize within a single reaction. The specific primers designed to detect four respective GM events (A2704-12, MON88017, Bt11, and MON863) were included in the tetraplex PCR system. Each of PCR products for four GM events could be distinguished by agarose gel based on their different lengths. The specificity and reproducibility of this multiplex PCR were evaluated. This multiplex PCR consistently amplified only a fragment corresponding to a specific inserted gene in each of the four GM events and also amplified all four of the PCR products in the simulated GM mixture. These results indicate that this multiplex PCR method could be an effective qualitative detection method for screening GM soy and maize in a single reaction.