MnSb, which is a ferromagnet with NiAs type crystal structure, is investigated by using the polarized neutron diffraction technique. Precise measurements of the magnetic structure factors give the following results: (i) The magnetic form factor of Mn on high angle reflections, which is sensitive to the asphericity of 3d-wave function, gives the unpaired electron population to be (0.89, 1.61, 1.22) for (ψxo, ψx±, ψu±) orbitals, respectively. These facts indicate that MnSb should be understood with a well overlapped 3d-subbands model proposed in the band calculation on NiS rather than the broadened 3d-level model proposed for MnAs(P) system. (ii) 3d-electron number of Mn is found to be four in MnSb on the basis of the asphericity of the magnetic form factor in conformity with the band calculation. (iii) Sb is magnetically polarized with moment of about 0.2 µb antiparallel to the total magnetization. © 1978, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.