Introduction: One factor affecting the degree of polymerization is the type of light-curing device. The aim of this study was to compare the effects of LED and QTH light curing units on the surface hardness of composite and compomer.

Materials & Methods: In this experimental study, 30 samples of composite and compomer were divided into 3 groups of 10 each. One-half of the subgroups in each group were cured with LED and the other half with Halogen light curing units (LCUs). 49 points on the surface were marked and then the hardness of these points was measured by using Vickers hardness test.

Results : The mean hardness of composites cured by using LED was more than the Halogen group but in compomer it was reversed and this difference was statistically significant (p<0.001). Z 250 composite had the highest level of hardness and the lowest hardness was related to the Heliomolar composite and had significant difference. (p<0.001)

 Conclusion :In the present study, the results indicated that LED light curing unit had great effect on the hardness of composites but in compomer, the QTH showed a better result.