Three-dimensional structure of insecticidal crystal proteins of Bacillus thuringiensis has been revealed to be three distinct domains. It has been found that different Cry toxins share similar structures. Domain Ⅰ, consisting of a bundle of α-helices in which a hydrophobic helix 5 is surrounded by 6～7 amphipathic helices, plays a unique role in pore formation. Domain Ⅱ, consisting of three antiparallel β-sheets with a loop at each apex, is responsible for receptor binding. Domain Ⅲ consists of two twisted, antiparallel β-sheets forming aβ-sandwich with a “jelly roll” topology, it might prevent the activated toxin from excessive degradation.