Objective To analyze the nucleotide sequences and genetic polymorphisms of UL138 gene of low passage human cytomegalovirus (HCMV) strains isolated from infants in Guangzhou province. Methods The low passage strains of HCMV were isolated from urine samples of 10 infants with HCMV infection in Guangzhou province and identified by multiplex PCR. The UL138 genes were amplified, cloned and identified with sequencing. The sequences were analyzed together with the homologous sequences of 10 clinical isolates published in GenBank. The sequences of UL138 genes were analyzed by using bioinformatics softwares for investigation of the post-translational modification sites, isoelectric points and second structures of UL138 proteins. Results Three low passage strains of HCMV (D2, D3 and D52) were isolated from infants with congenital HCMV infection. The complete sequences of UL138 genes of the three strains were submitted to GenBank after sequencing identification with the GenBank accession numbers of DQ180375, DQ180387 and DQ180359, respectively. The UL138 gene sequences of the three clinical isolates were highly conservative. Among the 841 base pairs of the UL138 gene sequences, mutations were identified in 16 sites with base substitution, no any insertion and deletion mutation was found. The 16 mutations resulted in 7 amino acid changes. No additional or deleted sites were found with regard to the post translational modification sites of UL138 protein in all clinical isolates except the Toledo strain. The isoelectric point of UL138 protein was 6.51 for all clinical isolates. Conclusion The UL138 genes and the deduced amino acid sequences of HCMV strains isolated from infants in Guangzhou were highly conservative, regardless of the polymorphism of UL138 gene. This study paved the way for further investigation on HCMV infection and its pathogenic mechanism. Key words: Human cytomegalovirus; Clinical isolate; UL138; Gene sequence; Polymorphism