Changes in the effect of temperature on microbial community composition (which included microbial diversity, abundance, and structure) and enzyme activities were measured at a bog peatland in North Wales, UK in spring (April), summer (August), and autumn (November), by using a thermal gradient bar. Microbial diversity (richness) and abundance were highest in summer. However, the activities of soil hydrolases (β-glucosidase, N-acetylglucosaminidase, Leu-aminopeptidase, and phosphatase) decreased in the order of autumn, spring, and summer, while arylsulfatase activity was highest in spring. Microbial community composition and enzyme activities showed seasonal differences in their responses to temperature. In spring, microbial diversity and abundance remained stable when temperature was below 14 °C, but increased with increasing temperatures above 14 °C. Microbial diversity in summer and autumn increased with increasing temperature; however, microbial abundance increased with increasing temperature in summer but decreased in autumn. Activities of β-glucosidase and Leu-aminopeptidase (but not those of the other enzymes) in spring and activities of all the examined enzymes in summer and autumn responded positively to increasing temperature. Our findings suggest that microbial diversity and abundance are strongly controlled by temperature and carbon availability, whereas enzyme activities are highly influenced by other environmental factors such as inhibitory compounds. Although microbial community structures in spring and autumn were more similar to each other than to those in summer, their responses to temperature rise differed substantially among seasons, suggesting hysteresis in microbial responses to temperature variations over a year period.