The structural, optical, magnetic and magnetoelectrical transport properties of p-type InMnP:Zn (Mn: 0.019–0.290 at.%) epilayers, which had been prepared by thermal diffusion of Mn through molecular-beam-epitaxial deposition of Mn onto InP:Zn epilayers grown by metal-organic chemical vapor deposition and subsequent annealing of the samples, were systematically investigated. For analyses of structural properties, it was observed that the x-ray diffraction peaks of MnO₂ for InMnP:Zn epilayers coincide with the P_4/2/mmm structure of MnO₂ proved by the electron diffraction analysis of transmission electron microscopy (TEM). For photoluminescence measurements, it was found that broad optical transitions related to Mn appear at 1.247 eV (E_v+0.173 eV) and 1.261 eV (E_v+0.159 eV), which are based on a band gap energy of 1.42 eV at 0 K. The samples revealed that in both the experimental pattern of TEM and the calculated diffraction pattern, {010} and {030} spots are missing, indicating that the FCC lattice was still maintained after the Mn doping. The forbidden, regularly spaced spots suggest the presence of a superlattice (a=11.738 Å), arising from the possible ordering of Mn atoms in the cubic structure of InP. The regularly spaced spots of ordered Mn produce the anomalous Hall effect (AHE) showing the characteristics of a diluted magnetic semiconductor (DMS), which is caused by hole-mediated ferromagnetism due to the increase of hole concentration in the tetrahedrally coordinated semiconductor. The transition from the ferromagnetic state to the paramagnetic state observed at ~150 K in AHE measurements was confirmed to be almost consistent with the ferromagnetic transition temperature (T_C) using superconducting quantum interference device measurements. These results suggest that an InP-based ferromagnetic semiconductor having relatively high T_C can be successfully formed based on InMnP:Zn epilayers in a category of DMSs.