Marek’s disease (MD), an immunosuppressive disease induced by Marek’s disease virus (MDV), provides an ideal model for studying diseases caused by a carcinogenic virus.  CD79B is a B-cell antigen receptor complex-associated protein β-chain precursor which is involved in the activation, proliferation, differentiation of B-cell and the transmission of downstream signals.  This study analyzed CD79B gene mRNA expression and methylation by two schemes #20 (5´ flanking to intron 1) and #27 (intron 2 to intron 3), between MDV-infected tumorous spleens (TS) and non-infected spleens (NS).  Results showed that average methylation levels of CpGs in #20 and #27 were higher in TS than in NS (P<0.05), while, CD79B mRNA expression was lower in TS than in NS (P<0.01).  Six of 40 CpG sites showed significantly (P<0.05) different methylation levels between TS and NS.  Correlation analysis showed that the average methylation level rather than a single site methylation level in #20 affected (P<0.05) mRNA expression.  Collectively, it was found that the change of CD79B gene expression after MDV infection might be partly explained by modification of DNA methylation.