Tetragonal stannous oxide (SnO) powders with different morphologies were solvothermally prepared from a single reactant in different solvents. Hydrazine hydrate (HZ), ethylenediamine, and their mixtures were employed as the solvents. The powders prepared in hydrazine hydrate and ethylenediamine are disc-like and spherical, respectively. In the mixed solvents, an evolution of crystal morphology between the disc and the sphere is observed while changing the volume ratio of the two constituents of the reaction media. The powders with different morphologies may have special applications as catalysts and coating materials.