Abstract: Objective To investigate the expressions of caspase-9 and Apaf-1 and their relationship with the apoptosis of keratinocytes in lichen planus （LP）. Methods Biopsy samples were resected from 30 patients with LP and 30 normal human controls. Terminal deoxynucleotidyl transferase （TdT）-mediated dUTP nick-end labeling （TUNEL） was used to examine the apoptosis of keratinocytes, immunohistochemistry to study the expressions of caspase-9 and Apaf-1 in samples. The mRNA expression of caspase-9 was detected with RT-PCR in 10 samples from patients with LP and 8 from normal controls. Results The apoptosis index of keratinocytes and mRNA expression of caspase-9 were higher in lichen planus than those in normal controls （75.67 ± 9.4 vs 38.15 ± 9.6, 2.30 ± 0.42 vs 1.60 ± 0.38, respectively, P < 0.05）. The positive units of caspase-9 and Apaf-1 were 14.45 ± 2.72 and 11.93 ± 3.14, respectively, in lichen planus, both of which were up-regulated compared with those in the normal controls （both P < 0.01）. Both the expressions of caspase-9 and Apaf-1 were positively correlated with the corresponding apoptosis index of keratinocytes （r1 = 0.96, 0.94, respectively, both P < 0.01）. Conclusions The accelerated apoptosis of keratinocytes is associated with the expressions of caspase-9 and Apaf-1, and may contribute to the formation and progress of lichen planus.