Lead selenide (PbSe) nanocrystals with different shapes were synthesized via solution-processing by adjustment of the reaction conditions. The prepared PbSe nanocrystals were characterized by X-ray diffraction and transmission electron microscopy. X-Ray diffraction pattern shows that the synthesized PbSe nanocrystals have cubic rock salt structure. The initial injection of precursors into hot reaction solvent immediately results in the formation of truncated octahedron-shaped nuclei, which are terminated by {100} faces and {111} faces. Acetate in the reaction mixture plays an important role in the formation of star-shaped PbSe nanocrystals. In addition, the reaction solvent also influences the shape of PbSe nanocrystals. Spindle-shaped PbSe nanocrystals are formed by spontaneous alignment and fusion of small quasi-spherical PbSe nanoparticles, namely, oriented attachment. The occurrence of oriented attachment of PbSe nanocrystals is the result of competition between the steric hindrance force and the orientation force. If the orientation force along some axes can overcome the steric hindrance force, the small PbSe nanocrystals with certain size distribution can self-assemble and evolve to spindle-shaped PbSe nanocrystals, vice versa, the small PbSe nanocrystals will grow individually to bigger quasi-spherical PbSe nanocrystals.