AIM:To observe the expression of pigment epithelium-derived factor (PEDF) in human lens, and discuss the correlation between the level of PEDF in human lens epithelial cells(LEC) and some lens-related pathophysiological conditions.METHODS: Lens anterior capsules attached with LEC were collected from cataract surgeries in patients with senile and congenital cataract. Human clear lens were obtained from eye bank. PEDF expression and location were detected in above frozen sections specimens by indirect immunofluorescence with polyclonal antibodies specific to human PEDF. Anterior lens capsules with LEC were respectively pooled, and grouped as following: clear lens, slight opacity, severe opacity, young and aged. In each group, PEDF protein levels were analyzed by Western-blot,and mRNA levels were determined by RT-PCR.RESULTS: PEDF protein was present in human lens, with mainly cytoplasmic expression in LEC. We firstly revealed the down-regulation of PEDF mRNA and protein levels in LEC, with the appearance and aggravation of senile cataract (P<0.01), and in aged cases as compared with young ones(P<0.01).CONCLUSION: The expression level of PEDF in LEC down-regulates with lens aging,cataract formation and progression.