Abstract: With the long-term large-scale cultivation of transgenicBtcotton, Bt proteins were introduced into the soil by means of plant organ residues and root exudates. Whether the residue and accumulation of Bt protein in soil will bring harm to farmland ecosystem hasgradually become the focus of public attention. In this paper, the residue of Bt protein in rhizosphere soil and the expression of Bt pro-tein in transgenic cotton roots and leaves in five areas of southern Shanxi province were analyzed by ELISA technology. The results showed that there were significant differences in Bt protein content between rhizosphere soil and non-rhizosphere soil in the five investi-gated areas. The highest Bt protein content in rhizosphere soil of transgenic cotton was 0. 184 8 ng / g, and the lowest was 0. 112 0 ng / g.It was suggested that there might be a low dose of Bt protein residues in the soil after transgenic Bt cottons were continuously planted.Furthermore, there were significant differences in Bt protein content between roots and leaves of transgenic cotton in the five regions ofsouthern Shanxi province. The highest Bt protein content in transgenic cotton roots was 19. 34 ng / g and the lowest was 12. 57 ng / g, while the highest Bt protein content in leaf was 128. 11 ng / g and the lowest was 83. 19 ng / g. The results showed that Bt protein content of transgenic cotton leaves was higher than that of roots in all sampling regions. This experiment research results will provide scientificbasis for reasonable cultivation of transgenic cottons and ecological safety evaluation of Bt crop

Key words: transgenic cotton, Bt protein, residue analysis, ELISA