Pesticidal activity of different Bacillus thuringiensis (Bt)$delta$-endotoxins, Cry1Aa, Cry1Ab, Cry1Ac and Cry2A, were investaged against Helicoverpa armingera infestig cotton crop worldwide. Cry1Ac toxin was found to be the most potent toxin towards H. armigera. All selected Bt toxins were found stable in viro processing by midgut juice of H. armigera. Saturation and Bt toxins were found stable in vitro processing by midgut juice of H. armigera. Saturation and competition binding experiments were performed with iodine-125 labeled proteins and brush border membrane vesicles prepared from the midgut of H. armigera. The results show saturable, specific and high affinity of all toxins expect for Cry2A. Both the toxis were bound with low binding affinity but with high binding site concentration. Heterologous competition experiments showed that Cry1Aa, Cry1A and Cry1Ac recognized or share the same binding site which is different from that of Cry2A. The data suggest that development of multiple toxin system in transgenic plants with toxin pyramiding, which recognize different binding sites, may be useful in the deployment strategies to decrease the rate of pest adaptation to Bt toxins in transgenic plants.