Novel photo-induced optical phenomena observed for AgX-intercalated mica compounds are presented, where X=NO3 , Cl, Br, or I. All compounds are newly synthesized and exhibit photochromism switched by alternate illumination with 0.3∼0.4 µm and 0.7∼0.8 µm light. AgNO3 -mica furthermore yields peculiar oscillatory phenomena under continuous illumination with ∼0.8 µm light. A hypothetical mechanism for these photo-induced effects is discussed on the basis of the nonlinear excitation and relaxation processes of AgX molecules sandwitched between mica layers.