Abstract: YANG Yong-mao*, JIA Mei, SHEN Min-juan, YANG Gui-lan, HAO Chun-mei, PAN Feng-jun. *Bayannaoer Hospital, Bayannaoer 015000, Inner Mongolia, China 【Abstract】 Objective To investigate the clinical feature and prevalence of chronic actinic dermatitis in a four-generation family with both monovular twins affected by chronic actinic dermatitis. Methods The clinical and laboratory findings from monovular twins simultaneously affected by chronic actinic dermatitis and their four-family members were analyzed. Results There were 76 members in the four-generation family, with 22 members （including 14 males and 8 females） diagnosed with chronic actinic dermatitis. No positive results were found from laboratory examinations or environmental survey. Conclusion Chronic actinic dermatitis was inherited in an autosomal mode in this family.