Abstract: The protection of the ability of Bacillus thuringiensis against ultraviolet irradiation by melanin produced by engineering bacterium Escherichia coli fss6 was studied.Results showed that the survival ratio of the B.thuringiensis under the protection of melanin was 8 times higher than that of those without melanin after UV irradiation.Melanin could protect the toxin protein from UV degradation significantly,the insecticidal activity of B.thuringiensis was improved as the concentration of melanin increased.