Molecular association has profound influences on the viscoelastic properties of polymers with associating side groups. The conventional wisdom is that interchain association dominates in the melt state, and the dynamics of the associative polymer network therefore might be understood by extending the classical molecular approaches such as the Rouse and reptation models for linear chains. Using small-angle neutron scattering and molecular dynamics simulation, here we show that while interchain association is important, intrachain association can not be neglected in determining the static structures of associating polymers in the melt state. Analyses of the radius of gyration, static structure factor, and intrachain mean-square distance of polymers with associating side groups have revealed a substantial deviation from the random walk structure at even moderate association strength and degree of functionality. This finding emphasizes the important role of intrachain loops in associative polymer networks.