We report the fabrication and investigations of organic light-emitting diodes (OLEDs) using a composite made by mixing poly[2-methoxy-5(2′- ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with CdSe/ZnS core/shell quantum dots (QDs). The electroluminescence efficiency of the studied devices was found to be improved as compared to devices using MEH-PPV. Moreover, the current density decreased with increasing QD concentration. We checked the effects of QDs on the electrical transport by determining the trap states, making use of the charge-based deep level transient spectroscopy (Q-DLTS) technique. The most striking result obtained is the decrease in trap density when adding QDs to the MEH-PPV polymer film. These results suggest that QDs would heal defects in nanocomposite-based devices and that CdSe/ZnS QDs prevent the trap center formation.