A significant increase in the growth of genetically modified organisms has been observed in recent years. As a result of the market introduction of these genetically modified (GM) crops in foods, legislation worldwide was prepared to deal with the question of the use and labelling requirements on GM crops and their derivatives. The aim of this work was to detect and to quantify GM soybean in soy-derived food products sold commercially in Florianópolis, Brazil, by polymerase chain reaction-based analysis. In total sixty-two samples of texturized soy protein and powdered soymilk were analysed and forty samples have been shown to contain Roundup Ready (RR) soy. Quantitative analysis revealed that only two out of these forty samples presented RR soybean content above 1%. These findings confirm the presence of RR soybean in Brazilian soy-derived food products and that the amount of samples with % RR content above 1% decreases when compared with previously published data.