An experimental investigation of the physical properties of light curing composite resin P-50 was performed, in which an argon ion laser beam was irradiated. The physical and mechanical properties of laser polymerized composite resin were determined by measuring the compressive strength, diametral tensile strength, curing depth and microhardness depending upon the experimental conditions such as the laser irradiation time(10sec, 20sec, 30sec) and laser power(300mW, 500mW, 1000mW). These observations were compared with a conventional visible light curing technique. In addition, to evaluate the marginal adaptation, Class V cavity was prepared on the buccal or lingual surface of the extracted premolar and filled with P-50 light curing resin. The test samples were irradiated with both light sources so that the interface between the restoration and the tooth structure were observed under scanning electron microscope. The most of physical and mechanical properties of the laser cured resin showed a remarkable improvement than those treated with the conventional light source, while the observations with the scanning electron microscope provided no significant difference for two polymerized sources. From the results in the experiment it appears that the potential of an argon ion laser is of important value of the use in the polymerization of composite resin.