In this study, we report the effect of the proportion of CdSe/CdS ultrasmall quantum dots (USQDs) conjugated on reduced graphene oxide (rGO). The proposed conjugation used a bond between the hydroxyl groups of the USQDs and the carboxylic groups of the rGO. The formation of the CdSe/CdS-rGO nanocomposites was confirmed by Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), fluorescence (FL), cyclic voltammetry (CV), and photocurrent response versus time (PR). The FTIR results confirmed the bond between the hydroxyl groups present in the CdSe/CdS USQDs with the carboxyl groups of the rGO and with a higher USQD proportion, and the interactions also occur in the epoxide and hydroxyl groups. HRTEM images confirmed the FTIR results. FL spectra of the nanocomposite exhibited a luminescence quenching with USQD proportion. The time-resolved fluorescence observed that the nonradiative decay rate is due to the electron transfer process, reducing lifetime. CV experiments showed that the USQD proportion increases on the rGO-promoted better reversibility of the peak of the Fe 3+ /Fe 2+ system. PR results showed a very weak photocurrent on the rGO when illuminated at 375 nm that increased with the increase of the nanocomposite. Therefore, we have demonstrated that it is possible to tune the optical and electrical properties of the rGO-CdSe/CdS USQD nanocomposites.