Abstract:[Background] The histone acetyltransferase general control nonderepressible-5 (GCN5) is a key epigenetic modifier that plays a role in regulating biological processes in eukaryotes. At present, little is known about the function and mechanism of GCN5 in Botrytis cinerea.[Objective] To analyze the function of BcGCN5 and lay a foundation for elucidating the function and regulatory mechanism of histone acetylation in the growth, development, and pathogenicity of B.cinerea.[Methods] The mutant ΔBcGCN5of B. cinerea was successfully constructed by gene knockout. The phenotype and pathogenicity of ΔBcGCN5 were analyzed with the wild-type strain B05.10 as the control.[Results] ΔBcGCN5 showed slow growth, reduced production of sclerotia and conidia, and diminished acid production, which ultimately led to weakened pathogenicity towards tomato fruits and tobacco leaves. [Conclusion] BcGCN5 positively regulated the growth, development, and pathogenicity of B.cinerea.