We report here the study of the optical limiting mechanism of phthalocyanine(H2Pc) and different kinds of metallo-phthalocyanine(MPc) in silica gel glass matrix. Prepared by sol-gel technique, the H2Pc or MPc doped silica gel glass composites were transparent and homogeneous with the required regular shape. The optical limiting behaviors of the composites were measured at 532 nm with 8 ns pulses. The results show that among three samples of H2Pc, NiPc or PbPc doped composites, PbPc has the most obviously optical limiting effect owing to the heavy atom effect. Besides, PbPc has better optical limiting properties in solid-state silica gel glass matrix than in liquid-state DMF solution. Fluorescent ZnTSPc or GaPcCl doped composites have little optical limiting effect. The reasons are discussed from the view of excited physical process and the implied mechanism is given.