Increasing urbanization is creating novel environments to which animals must adapt. The process and the consequence of urbanization have been the topic of growing concern for evolutionary biologist. Although many studies showed the relationship between urbanization and morphology, physiology, and behavior, the driving force is unclear yet. So-called, credit card hypothesis proposed that among environmental factors, food resources and predation pressures are the important driving factors. Predictable food resources and low predation pressures would enable low competitive individuals to live in the urban populations though only high-competitive individuals can survive in the rural populations. However, there is only one study testing this hypothesis but failed to validate. Here, using house finches, Carpodacus mexicanus, we tested the credit card hypothesis by the aggression trials in which urban and rural males competed for resources. Although the credit card hypothesis is only based on natural selection via food resources and predation pressures, sexual selection may also affect on the results. Thus, colorful breast plumage, a sexually selected trait in this species, was taken into account in the present study, and will be discussed whether the credit card hypothesis can explain the observed pattern.