The aims of this study are to investigate the effect of light intensity and curing time on the degree of conversion and amount of residual monomer released from poly-acid modified composite resin samples cured with QTH light curing unit.Single light cured poly-acid modified composite resin restorative material Glasiosite Caps (VOCO/ Cuxhaven, Germany) (n=130 samples divided to the groups ) exposed to different exposure times (10, 30 and 40 seconds) and at different light intensities (410 and 490 mw/cm²). The degree of conversion of poly-acid modified composite resin samples was investigated by Fourier transform infrared spectroscopy (FTIR). While the amount of residual monomer released from poly-acid modified composite resin samples was investigated through measuring the released residual monomer in doubled distilled water with (CECIL 2000) Ultraviolet visible spectrophotometer.