The detection of Genetically modified (GM) food is necessary due to food safety regulations, and the labelling of GM-food will be practiced by 2003 in Taiwan. In this study, products such as soyamilk, tofu, dried tofu, yaba, su-ju, soyabean protein, vegetable meat and vegetable soyabean made of Roundup Ready Soyabean (RRS) were screened by multiplex polymerase chain reaction. By this method, the limit of detection for reference samples containing 5% (w/w) RRS of products soyabean, soyamilk, tofu, dried tofu and yaba was determined. This method can be used for detection of su-ji and soyabean protein efficiently but not vegetable meat due to its DNA degradation. We also found that no RRS gene been detected in vegetable soyabean harvested in Taiwan.