In order to investigate stability of the cry1Ab gene and resistance in the T-1 generation of transgenic cotton (Gossypium hirsutum var. Coker 100), transgenic seeds were analyzed by PCR, Southern and Western blotting and bioassayed. Seed samples from transgenic lines (T-0) along with seeds from non-transgenic lines s as control were used. PCR analysis showed the presence of cry1Ab gene in 63 out of the 150 T-1 plants. Integration of the cry1Ab gene into the genome of transgenic plants was confirmed by Southern blotting. Western immunoblot analysis of transgenic plants revealed the presence of a band with MW of 67 kDa using anti-Cry1Ab-polyclonal antiserum. Bioassay tests indicated that the Cry1Ab protein was active and that the larvae died in the first days. Significant differences were observed in the mortality rate, growth rate and extent of damage on the leaves between the transgenic and non-transgenic plants. The average mortality of the larvae in line 17 was 100%, in comparison with the control. These results indicated the relative advantage of line 17, which carries one copy of the cry1Ab gene in comparison with the other lines.