Trade-off between early reproduction and longevity has been shown to play an important role in a theory of life history and senescence. Under crowded treatment, Daphnia magna depresses somatic growth and more invests reproduction. In this study, D. magna reduced its body size at maturity, produced large size offspring, and shortened its longevity under crowding condition. This implies a trade-off between longevity and fecundity under crowding condition. It is well known that Heat shock proteins (HSP) are related to lifespan, and that Vitellogenin(VTG) provides the major egg yolk proteins during vitellogenesis. In this study, hsp70 gene expression was lowered, while vtg1 gene expression was promoted under the crowding condition. This antagonistic relationship between hsp70 and vtg1 in D. magna suggests more investment to reproduction but reduces longevity under crowding condition.