Objective To quantify the expression levels of calpain 1 and caspase-3 in lichen planus (LP) lesions and their relationship with the apoptosis in keratinocytes.Methods Biopsy samples were obtained from the lesions of 20 patients with LP and normal skin of 10 healthy controls,and embedded in paraffin.Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) was used to evaluate the apoptosis in keratinocytes,and immunohistochemical staining to detect the expressions of calpain 1 and caspase-3,in these tissue specimens.Data were processed by SPSS 13.0 software.Comparison analysis was carried out by t test for apoptosis index,and by rank sum test for the expressions of calpain 1 and caspase-3.Spearman correlation analysis was conducted to evaluate the relationship between these parameters.Results The apoptosis index of keratinocytes was higher in LP lesions than in the normal skin (67.59 ± 13.50 vs.28.26 ± 7.56,t =8.52,P ＜ 0.01).Significantly increased expressions of calpain 1 and caspase-3 were observed in the epidermis of LP lesions compared with the normal skin (T =78.00 and 77.00,respectively,both P ＜ 0.01).The expressions of both calpain 1 and caspase-3 were positively correlated with apoptosis index of keratinocytes (r =0.71 and 0.74,respectively,both P ＜ 0.01).Conclusions The expressions of calpain 1 and caspase-3 are upregulated in LP lesions,which may be closely associated with the accelerated apoptosis in keratinocytes.