Objective: To explore the relationship between the PTCH1 mutation and the expression of bcl-2, filaggrin, and loricrin in the keratocystic odontogenic tumour (KCOT), as well as the effects of the mutated PTCH1 on the epithelial proliferation and differentiation.Methods: The samples were collected from 20 cases of KCOT with mutated PTCH1, as well as 20 cases without mutation.All the samples were analyzed with immunohistochemical staining, for the purpose of investigating the expression of bcl-2, filaggrin, and loricrin.Results: In the samples with mutated PTCH1, the epithelia of 60% (12/20) cases expressed intensively positive bcl-2 staining, 20% (4/20) expressed moderate staining, and 20% (4/20) weak staining, but no negative bcl-2 staining samples were investigated;it was significantly different from the samples without PTCH1 mutation, in which 20% (4/20) expressed intensive staining, no moderate staining, 50% (10/20) weak staining, and 30% (6/20) negative staining were investigated (U=72, P=0.001).For the expression of filaggrin, 55% (11/20) of samples with PTCH1 mutations were stained weakly and 45% (9/20) showed negative staining, while in the samples not harboring PTCH1 mutations, 30% (6/20) cases showed moderate positive staining, 40% (8/20) weak staining and 30% (6/20) negative staining, no intensive staining was investigated (U=182, P=0.48).The loricrin expressed in all the layer of the epithelia in all the samples, while the filaggrin was mainly loca-lized within 1-4 layer cells of the epithelia.The differences of the expression of filaggrin and loricrin between the samples with mutated PTCH1 and without mutated PTCH1 displayed no significance.Conclusion: In the epithelia of KCOT, the bcl-2 expression was significantly associated with the PTCH1 mutation, which suggested that the mutated PTCH1 gene perhaps promotes the proliferation of KCOT epithelium.