The changes in surface morphology and crystal orientation of electrodeposited tin from acid stannous sulphate solutions containing 1 mM N,N-bis(tetraoxyethylene)octadecylamine (TOOA) and various concentration (0.2-2 mM) of benzalacetone (BA) have been studied as functions of electrolysis time or BA concentration by electrochemical methods, scanning electron microscopy and X-ray diffractometry. The inhibitory effect on the reduction of the tin (II) ion became stronger with increasing concentration of BA. In the presence of both TOOA and BA, when electrolyses were carried out at the more negative potentials than the reduction potential of BA, the reduction product of BA induced reticular crystals (network structure) of tin over the whole surface. This structure appeared in the early stage of electrolysis and exhibited an intense (200) diffraction peak. On the other hand, the crystal grain size and the surface roughness of electrodeposited tin became smaller with increasing concentration of BA from 0.2 to 2 mM. Further, fine-grained and smooth electrodeposits of tin were obtained from acid stannous sulphate solutions containing TOOA and high concentration of BA due to the synergistic effect of these adsorbed species.