We have investigated the light-emitting diodes based on colloidal CdSe quantum dots (QD-LEDs), in which inorganic ZnSnO thin films and organic TPD thin films were used as the electron-transporting layer (ETL) and hole-transporting layer (HTL), respectively. The quantum dots were embedded between the inorganic ETL and organic HTL to form a sandwich structure. ZnSnO ETL was made by magnetron sputtering, while the TPD and QD films were made by spin-coating method. The QD-LEDs display sharp interface and smooth morphology. Optical and electrical characterizations show that QD-LEDs have low turn-on voltage, good monochromaticity, bright electroluminescence and good stability in atmosphere ambient. These characteristics are attributed to the utility of high electron mobility and low carrier concentration of the ZnSnO films used as the ETL. To investigate the devices operation mechanism, the conductivity of ZnSnO was varied during deposition to realize equal injection rate for both electrons and holes, which allows the device to operate optimally.