Abstract: Objective To explore the expressions of costimulatory molecule B7-H1 in malignant cutaneous tumor tissues and their clinical significance. Methods The expressions of B7-H1 were detected by ElivsionTM plus immunohistochemical technique in tumor tissues from 51 patients with squamous cell carcinoma （SCC group） and 93 patients with non-squamous cell carcinoma. Tissues obtained from 10 patients with actinic keratosis （precancerous lesions group） and 10 patients with benign cutaneous tumors （benign tumor group） were chosen as control. The positive rates of B7-H1 in precancerous lesions group， benign tumor group， SCC group and non-squamous cell carcinoma were analyzed. The relationships between expressions of B7-H1 and clinicopathological characteristics （age， sex， tumor size， tumor location， exposure， location and degree of differentiation） in SCC were investigated. Results The B7-H1 was characterized by diffuse brown staining and mainly expressed in cell membrane and cytoplasm. The positive rates of B7-H1 in precancerous lesions group， benign tumor group and SCC group were 10.0％ （1／10）， 40.0％ （4／10） and 76.5％ （39／51）， respectively. There was no significant correlation between expression of B7-H1 and clinicopathological characteristics. The B7-H1 was also expressed in common epithelial origin non-squamous cell carcinoma， including basal cell carcinoma， sweat gland carcinoma， Paget’s disease， adenoid cystic carcinoma and sebaceous carcinoma with positive expression rates of 81.4％ （35／43）， 70.0％ （7／10）， 100.0％ （3／3）， 100.0％ （2／2）， 100.0％ （1／1） and 76.2％ （16／21）. No expression was observed in the non-epithelial origin bulge fibrosarcoma.Conclusion B7-H1 is involved in the carcinogenesis and development of malignant cutaneous tumor.