Ecological information on inconspicuous, small, fossorial, and nocturnal snakes is very limited. We investigated seasonal activity patterns of Achalinus spinalis, a small, nocturnal, and fossorial snake endemic to East Asia. We also examined factors that affect its activity pattern above the ground. The seasonal activity of the snake showed a bimodal pattern, which peaked in early summer and autumn. Males were more active than females in early summer. Gravid females were captured in May and July, but we did not find any gravid females in June. Effect of temperature on the snake activity was found in autumn, and a positive relationship between snake activity and prey (earthworms) abundance was detected in early summer. The prey items were confirmed from eight snakes, and half of the diet records were obtained in June. The annual activity pattern of A. spinalis was concordant with that in other species of temperate snakes. However, the activity of juvenile snakes is considerably different from that of temperate snakes: hatchlings of A. spinalis remained underground and did not actively move after hatching until emergence from their first hibernation early the following summer.