Bis[2-(aminomethyl)pyridine]platinum(II) chloride monohydrate [Pt(amp)(2)]Cl-2.H2O has been found to exhibit photochromism in single-crystalline phase. Single crystals of the chloride were changed from almost colorless to pale-blue by the irradiation of the light. Its aqueous solution, however, shows no photochromic behavior. Absorption bands induced by the irradiation of the light show dichroism in the single crystals. The photochromic behavior of the present platinum complex chloride is very interesting, because it occurs in single-crystalline phase but not in solution.