DNA methylation is an important epigenetic regulatory mechanism that influences genomic stability, gene activation, X-chromosome inactivation and other factors. A change in DNA methylation is usually associated with aging and cellular senescence. DNA methyltransferase 1(DNMT1) is the most abundant DNA methyltransferase, and it plays an important role in maintaining the established methylation pattern during DNA replication in vertebrates. Although the effect of aging on DNA methylation has been well studied in vertebrates, little research has been conducted in invertebrates, especially in marine bivalves. In this study, we examined global DNA methylation levels in four groups of adult Zhikong scallop Chlamys farreri at different ages. The results showed that both the age and tissue type had a strong effect on the DNA methylation. In addition, a significant decrease in DNA methylation with aging(1–4 years) can be detected in mantle, kidney and hepatopancreas. We further measured the change in DNMT1 transcript abundance using quantitative reverse transcription PCR(q RT-PCR), which revealed that DNMT1 transcription significantly decreased with aging in mantle and hepatopancreas and strongly correlated with DNA methylation(R = 0.72). Our data provided greater insight into the aging-related decline of DNA methylation, which could aid in gaining a better understanding of the relationship between DNA methylation and the aging process in bivalve mollusks. DNA methylation is an important epigenetic regulatory mechanism that influences genomic stability, gene activation, X-chromosome inactivation and other factors. A change in DNA methylation is usually associated with aging and cellular senescence. DNA methyltransferase 1 (DNMT1) is the most abundant DNA methyltransferase , and it plays an important role in maintaining the established methylation pattern was DNA well in vertebrates, little research has been conducted in invertebrates, especially in marine bivalves. In this study , we examined global DNA methylation levels in four groups of adult Zhikong scallop Chlamys farreri at different ages. The results showed both are the age and tissue type had a strong effect on the DNA methylation. In addition, a significant decrease in DNA methylation with aging (1-4 years) can be detected in mantle, kidney and hepatopancreas. We further measured the c hange in DNMT1 transcript abundance using quantitative reverse transcription PCR (q RT-PCR), which revealed that DNMT1 transcription was decreased with aging in mantle and hepatopancreas and strongly correlated with DNA methylation (R = 0.72). Our data provided greater insight into the aging -related decline of DNA methylation, which could aid in gaining a better understanding of the relationship between DNA methylation and the aging process in bivalve mollusks.