Abstract: The objective of this study is to reveal the tempo-spatial distribution of Cry1Ab/c protein in main stem leaves of transgenic cotton variety M-49 and X-37. The Cry1Ab/c protein content and the water-soluble protein in the main stem leaves from transgenic Bt cotton were detected by enzyme linked immunoassay（ELISA）and Coomassie brilliant blue method，respectively. The results showed that the content of Cry1Ab/c protein in the main stem leaves of the cotton variety X-37 were greatly higher than that in M-49. The contents of Cry1Ab/c protein in both varieties increased gradually from the top leaves to the bottom leaves. The Cry1Ab/c protein content of the bottom leaves were greatly higher than that of the top leaves at squaring period（3 June 2016）and initial flowering stage（27 June 2016）（P < 0.05），but there were no significant differences on the content of Cry1Ab/c protein between the upper and middle parts of the main stems at blossoming and boll forming stage（6 August 2016）and boll period（26 August 26 2016）. Besides，the proportion of the Cry1Ab/c protein content to the water-soluble protein content in the upper leaves were greatly higher than that in the middle and lower leaves in main stem of transgenic Bt cotton（27 June 2016）. In summary，the content of Cry1Ab/c protein in the main stem leaves of both varieties decreased gradually from the bottom leaves to the top leaves，and the trend of the content of Cry1Ab/c protein lowered after increased with its growth period going on，and the ratio of the Cry1Ab/c protein to the water-soluble protein content from the upper leaves changed more significantly at initial flowering stage than other developmental stages.

Key words: transgenic Bt cotton, Cry1Ab/c protein, ELISA, temporal and spatial distribution, water-soluble protein