InN films have been grown on GaP(111)B substrate using metalorganic chemical vapor deposition (MOCVD). Nitridation effects of GaP(1 1 1)B substrate on MOCVD growth of InN have been clarified. It is revealed that single crystalline InN films can be obtained on GaP(1 1 1)B only when the nitridation of the substrate is not made intentionally. InN films grown on nitrided GaP(1 1 1)B are found to be polycrystalline. XPS analysis shows the formation of PNx as well as GaN after the nitridation of GaP(1 1 1)B substrate surfaces by flowing NH3 above 500 degrees C. Formation of PNx is responsible for the poor crystalline structure of InN. Differences in nitridation behavior between GaP and GaAs are also discussed.