Acorn masting is a typical resource pulse that generates community-wide effects on forest ecosystems. Forest-dwelling rodents are considered as a key-player of the effects. Although the increase in rodent density after masting has been frequently observed, its dynamical processes remain unclear. To examine changes in life-history traits of rodents (age/size at sexual maturity) under the fluctuation of acorn abundance, we conducted capture-recapture surveys for the Japanese wood mouse Apodemus speciosus during 2010–2019 in a secondary forest in Iwate, northern Japan, in which the konara oak Quercus serrata dominated. Growth curve was estimated for 21 spring-born female mice, and age/size at sexual maturity were determined using capture-history. The growth and maturation pattern of female mice varied among yearly cohorts; mice born after acorn-rich years stopped somatic growth at smaller size (average, 29.1 g) than those after acorn-poor years (34.8 g); and they reached sexual maturation earlier in age and smaller in size. This finding suggests that wood mice can alter life-history traits according to acorn abundance. Since acorns were unavailable in their growing period (May–September), the observed effects of acorn masting on growth patterns may be caused through improved conditions of mother mice; they were heavier after acorn-rich years.