Анотация: Classical swine fever (CSF) is caused by classical swine fever virus (CSFV), a member of the genus Pestivirus of the family Flaviviridae, and engender important economic ramifications. Our previous study reported that both CSFV Group 1 and Group 2 were both contributed to the epidemic of CSF in mainland China, and showed the trend of switch from Group 1 to Group 2. In order to investigate the relationship between epidemiological trend and evolutionary rate of two Groups, the E2 glycoprotein gene (located in 2508-2697) of 68 CSFVs isolated from mainland China during 1982-2009 were aligned, and Bayesian Markov Chain Monte Carlo (MCMC) analysis was performed. The results indicated that the mean evolutionary rate of Group 2 (3.6861x10-3 substitutions per site per year (subs/site/year)) evolved much faster than Group 1 (4.9852x10-4 subs/site/year). We presumed that the differences in evolutionary rates of two groups likely implied that Group 2 possessed higher mutation rate and experienced higher selection pressure, however the real mechanism for the diversity in the evolutionary rate requires further investigation