Fungal chitin synthase of classes V and VI (or VII), which contain an additional N-terminal myosin motor domain, have been shown to play important roles in pathogenesis. To study the function of BcChsVI in Botrytis cinerea, BcChs6 gene was disrupted through Agrobacterium tumefaciens-mediated transformation. The Bcchs6 disruption mutant exhibited a 45.5 % increasing in its chitin content when compared with wild strain. The qRT-PCR analysis revealed that in Bcchs6 mutant the expression of BcChs6 was significantly decreased, while the expression of BcChs2 and BcChs3a was increased when compared with wild type. It is probable that the disruption of this gene provoked a compensatory mechanism regulating the cellular response to cell wall damage. Interestingly, the radial growth of Bcchs6 mutant was drastically reduced when 50 % solute was removed from the regular PDA medium, and they were more sensitive to Calcofluor white and other cell wall disturbing chemicals. Pathogenicity assays on tomato leaves indicated that they were significantly reduced in their ability to cause disease. Our results demonstrated that BcChs6 is necessary for proper hyphal growth and pathogenicity of B. cinerea on tomato leaves.