Abstract： Objective To investigate the effect of acitretin on the histopathology and ultrastructure of lesions from patients with bullous ichthyosiform erythrodermia (BIE), and to explore mechanisms underlying the modulation of keratinization process by acitretin. Methods Lesional tissue was obtained from the back of 4 patients with BIE before and after the treatment with acitretin. Light microscopy and transmission electron microscopy were performed to observe histopathological and ultrastructural changes in these lesions. Results After treatment, the improvement in clinical manifestations was more than 75% in all the 4 patients, and reached 90% in 1 of the 4 patients. As histopathology and ultrastructural study showed, there was an obvious improvement in hyperkeratosis and continuity of extra cellular lamellar membrane, and a decrease in keratin deposition in prickle and granular layer, but no remarkable changes were observed for the proliferation of prickle cells or acantholysis. Conclusions Acitretin shows a favorable efficacy in clinical treatment of BIE,with histopathological and ultrastructural improvement mainly located in the stratum corneum. The modulation of keratinization process in keratinocytes by acitretin appears more apparent in granular and corneum layers.