The incorporation of (Bt) rice straw into fields may influence the growth of subsequent crops, but its ecological risks for winter vegetables remain largely unreported. Investigating the effects of Bt rice straw extracts on the seed germination and plant growth of pakchoi ( L. ssp. Makino var. Tsen et Lee) can provide a theoretical foundation for ecological risk assessments. In this study, straw extracts from non-Bt rice (Tianyouhuazhan), homozygous Bt rice (T775), and heterozygous Bt rice (F of T775 hybrid) were used as experimental materials at concentrations of 10, 20, and 40 g·L. Results showed that, compared to non-Bt extract, 40 g·L homozygous Bt extract increased seedling height and leaf peroxidase (POD) activity but inhibited catalase (CAT) and root superoxide dismutase (SOD) activities. The 20 g·L extract boosted root CAT activity yet suppressed leaf CAT and POD activities. The 10 g·L extract enhanced root length but reduced leaf CAT and POD activities. The 40 g·L heterozygous Bt extract increased leaf and root POD activity but inhibited germination rate and leaf SOD activity. The 10 g·L extract promoted root length and seedling POD activity but suppressed leaf POD activity. In plant growth assessments, the 10 g·L homozygous Bt extract reduced underground dry weight, and the 10 g·L heterozygous Bt extract inhibited both above and underground dry weight, while the 20 g·L heterozygous Bt extract increased aboveground dry weight. In conclusion, the effects of homozygous and heterozygous Bt rice straw extracts on pakchoi varied with concentration and physiological indices, showing no clear pattern. Optimizing straw return concentrations based on Bt rice variety differences is essential to mitigate ecological risks.