Abstract.-The fecundity and rate of maturity of yellow perch (Perca flavescens) were examined in relation to age and size. Samples were obtained from native and experimental populations in small lakes and ponds in lower Michigan. Fecundity was more strongly related to parental weight or length than to age. Attainment of sexual maturity was a function of sex, length, and age, with the older and larger individuals more likely to be mature. For males, which mature sooner than females, the smallest mature specimen was 61 mm and the largest immature fish was 106 mm. Males matured after one growing season unless growth was unusually poor. For females, the smallest mature specimen was 86 mm and the largest immature fish was 180 mm. Females rarely matured after one growing season but most had matured after four. The study populations matured sooner and were less fecund than yellow perch populations cited in the literature (mostly in the Great Lakes) but were similar to some populations of European perch.