Abstract: Objective To analyze genetic characteristics and transmission patterns of human immunodeficiency virus type1(HIV-1) CRF01_AE strains isolated in Dalian municipality in recent years.Methods Viral RNA was extracted from plasma samples,HIV-1 genes(env) were amplified by reverse transcriptase and nested-PCR using specific primer pairs.PCR products were sequenced and analyzed with phylogenetic method.Results A total of 26(63.41%) HIV-1 subtype CRF01_AE sequences were identified from the 41 samples successfully sequenced.All of the HIV/AIDS patients positive to CRF01_AE strains were infected through sexual contacts.Two main epidemic clusters,the men who have sex with men(MSM) cluster and the heterosexualit(Hetero) cluster(infected through heterosexual contact),were identified in the CRF01_AE strains in Dalian.Genetic distance analysis showed that the diversity of MSM cluster was obviously less than that of Hetero cluster and it was found that no international reference strain was closely correlated with the two clusters.The MSM cluster presented close relations with MSM strains form Liaoning province,Beijing and Jilin province;the Hetero cluster presented the close relations with homosexual strains from Liaoning province,Beijing and heterosexual strains from Southeast Coastal provinces.Conclusion The CRF01_AE strains are the dominant subtypes and homosexual transmission is the major route of transmission of the strains isolated in Dalian.The CRF01_AE strains of Dalian originated in Thailand and there were two or more transmission patterns in Dalian,and seemed to have had several events of epidemics in populations with the CRF01_AE strains isolated in MSM of northern region of China.