Abstract: Objective To investigate the status of single nucleotide polymorphism(SNP) of interleukin-12p40(IL-12p40) 3' untranslated region(3' UTR)+1188(A/C) site and cytomegalovirus infection in infants,and to find the association of IL-12p40 genetic polymorphism with human cytomegalovirus(HCMV) infection.Methods Infants with activa HCMV infection(n=125),infants with latent HCMV infection(n=108),and healthy controls(n=110) were genotyped and analyzed for the SNP of IL-12p40+1188(A/C) using polymerase chain reaction-restriction fragment length polymorphism(PCR-RFLP) and DNA sequencing.HCMV DNA in urine of the infants with active HCMV infection were analyzed using fluorescence quantity-polymerase chain reaction(FQ-PCR).Results The frequency distribution of AA,AC and CC genotype of IL-12p40+1188(A/C) site in the infants with active and latent HCMV infection and healthy controls existed a significant difference(χ²=10.542,P=0.032).Frequencies of A and C allele of IL-12p40+1188(A/C) site were 52.8% and 47.2% in the infants with active HCMV infection,63.4% and 36.6% in the infants with latent HCMV infection,and 67.7% and 32.3% in the control group,with significant differences among the three grouops(χ²=11.777,P=0.003).There were significant differences in the allele frequency distribution between the infants with active HCMV infection(χ²=10.930,P=0.001; odds ratioOR_A=0.805,95% confidence intervalCI:0.703-0.922; OR_C=1.372,95% CI:1.141-1.650).There were significant differences of HCMV DNA in urine in AA,AC and CC genotype of the infants with HCMV active infection(F=9.325,P=0.006).Conclusion There is a relationship between SNP of IL-12p40+1188(A/C) site and the susceptibility to HCMV infection,and the carriers with C allele may be susceptible to develop active HCMV infection.