Asymmetric particles of NaCl and KCl crystals have been obtained by using a crystallization method. The particles were produced by precipitation at the solution-1-butanol interface. The two solvents are essentially immiscible, but have slight mutual diffusion. When the aqueous solution contacts with 1-butanol, the interfacial area becomes supersaturated, resulting in nucleation and particle growth in the interfacial zone. The asymmetric particles featured a stepped surface on the side in contact with 1-butanol. The other surfaces in contact with the aqueous phase were a flat cubic structure. Precipitated NaCl particles showed very clear asymmetric structure. However, some of KCl particles had less well-defined structures. This is due to the high diffusion rate of hydrated K ions and the fast diffusion results in a supersaturated state around the interface. This situation can be explained by a model of crystal growth based on solute clusters in supersaturated solutions.