The purpose of this study was to evaluate the compensation effect of exposure duration increase to decreased light intensity of visible-light curing unit. The specimen with 2mm thickness was made of Restorative $Z-100^{TM}$ (A2 shade, 3M Dental Products, U.S.A.) and cured with $Optilux^{TM}$ (Demetron Research Co. U.S.A.). The light intensity was controlled to 420 $mW/cm^2$, 540 $mW/cm^2$, 630 $mW/cm^2$ and curing time, also, controlled to 40, 60, 80 seconds. Cured specimen was stored in a light-proof container for 24 hours to post-irradation was completed. Microhardness of top and bottom surface of specimen were measured to evaluate the depth of cure. The obtained results were as follows: 1. The microhardness of top and bottom surface of the composite resin specimen was increased significantly as light intensity and exposure time was increased (P<0.01). 2. Light intensity was more correlated with bottom microhardness(${gamma}{geq}$0.438) than top microhardness(${gamma}{geq}$0.213), and exposure time was more correlated with top microhardness (${gamma}{geq}$0.424) than bottom microhardness(${gamma}{geq}$0.335). 3. The regressive equation was obtained in this study as follows : $H=0.07{ imes}D+0.012{ imes}I+76$ (H : Microhardness(KHN), D : Exposure time, I : Light intensity)