Objective: This study aims to investigate the influence of light curing unit on micro-hardness and degree of conversion of two resin composite materials. Method: A total number of 160 resin composite specimens were divided into two equal groups (n=80) according to the two commercial brands of resin composite selected; nanofilled or microhybrid resin composite. Each group was further subdivided into two equal subgroups (n=40) according to the type of curing unit used; quartz tungsten halogen (QTH) or light emitting diode (LED) curing unit. Then each subgroup was divided into two equal classes (n=20) according to the tested methodology; assessment of micro-hardness or degree of conversion. Surface micro-hardness was measured using Vickers micro-hardness tester after 15 min, 24 hours and 1 week. Degree of conversion of the uncured and cured specimens was assessed using Fourier transformation infrared (FTIR) spectrophotometer unit. The results were collected, tabulated and statistically analyzed. Results: For the micro-hardness results, regarding nanofilled composite specimens, cured with LED at the top surface, 24 hours period showed the statistically significantly highest mean micro-hardness value. __________________________________________________ Regarding microhybrid composite cured with LED at the top surface; 24 hours period showed the statistically significantly highest mean micro-hardness. For the mean values of degree of conversion, microhybrid composite cured with LED showed the statistically significantly highest mean degree of conversion. Nanofilled composite cured with QTH showed the statistically significantly lowest mean degree of conversion. There was no statistically significant correlation between micro-hardness and degree of conversion. Conclusion: The effect of light curing unit on degree of conversion and micro-hardness was found to be material dependent. The aging procedures resulted in a significant decrease in micro-hardness values. There is no correlation between degree of conversion and micro-hardness.