We report 31P NMR measurements under various magnetic fields up to 7 T for the intermediate valence compound EuNi2P2, which shows heavy electronic states at low temperatures. In the high-temperature region above 40 K, the Knight shift followed the Curie-Weiss law reflecting localized 4 f states. In addition, the behavior corresponding to the temperature variation of the average valence of Eu was observed in the nuclear spin-lattice relaxation rate 1=T1. With the occurrence of the Kondo effect, 1=T1 was clearly reduced below 40 K, and the Knight shift becomes almost constant at low temperatures. From these results, the formation of heavy quasiparticles by the hybridization of Eu 4 f electrons and conduction electrons was clarified from microscopic viewpoints.