The purpose of this study was to investigate the curing effect of visible light through tooth substance, 0.5mm, 1.0mm thickness of enamel and dentin were prepared. Experimental specimen were made by Bisfil M & Silux packing into cylindrical brass mold 6.0mm in diameter, 2.0mm and 3.0mm, in height. All specimen were irradiated by visible light (Grip type) model No. SDL-50 Shofu Co.) for 30 seconds through tooth substance. Experimental groups were classified into enamel group (group 1) and dentin group (group 2) according to the thickness of tooth materials and then were divided into 2 subgroups (0.5mm group and 1.0mm group). In experimental groups, visible light irradiated to the specimen through either 0.5mm in thick or 1.0mm in think of tooth material. In Control group specimen were prepared by direct irradiation on the specimen surface of visible light without through tooth substance. The hardness was measured with a Barcol hardness tester (Barber-Colman Co. U.S.A.) for each prepared specimen. The results were as follows: 1. In control group, there were higher hardness values than those of in experimental group. 2. In experimental groups, 0.5mm groups had higher hardness values than 1.0mm groups did. 3. The hardness value at top surface of the specimen were higher than the hardness of bottom surface in each group. 4. Bisfil M had higher hardness values than Silux. 5. In all specimen of 3.0mm height polymerization effect was not occurred at bottom surface except Bisfil M in control group.