Three kinds of Ni and Al powder mixtures with nominal composition Ni75Al25 were employed to prepare Ni3Al alloys by spark plasma sintering(SPS) process. The raw powders include fine powder, coarse powder and mechanically-alloyed fine powder. The effects of powder characteristics and mechanical alloying on structure and properties of sintered body were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), bending test and Vickers hardness measurements. For all mixture powders near fully dense Ni3Al alloys (relative density＞99.5%) are obtained after sintering at 1 150 ℃ for 5 min under 40 MPa. However a small fraction of Ni can be reserved for alloy from coarse powders. The results reveal that grain size is correlated with particle character of raw powder. Ni3Al alloy made from mechanically-alloyed fine powder has finer and more homogenous microstructure. The hardness of all alloys is similar varying from HV470 to 490. Ni3Al alloy made from mechanically-alloyed fine powder exhibites higher bending strength (1 070 MPa) than others.