Whiskers of AgX, 1-10 μm long, were formed on alginic acid films by immersion of glass-supported silver alginate films at room temperature in HX solutions ranging in concentration from 0.01 to 0.1 M. All the whiskers grew in a direction nearly perpendicular to the surface of the polymer films, but they differed appreciably from one another in shapes and dimensions. The orientations of the whiskers were examined by X-ray diffraction method. In the cases of silver chloride and silver bromide, the whiskers were preferentially oriented in the {111} directions, which were nearly perpendicular to the film surfaces. The whiskers of AgI were also oriented in the direction of the c -axis in a similar manner. The conditions and the rates of formation of the whiskers were also studied.