The operating mechanism, particularly the carrier injection mechanism, of a hybrid organic-inorganic light-emitting diode (HOILED) is reported. Asymmetric hole injection has been observed in a symmetric hole-only device, which has two identical interfaces between a conducting polymer and a metal oxide. A HOILED having a layer of molybdenum oxide (MoO3) deposited on a layer of poly(dioctylfluorene-alt-benzothiadiazole) (F8BT) demonstrated a markedly enhanced hole injection, four orders of magnitude higher on one side of the structure than on the other side. This enhanced hole injection is the considered to initiate the operation of the HOILED. X-ray photoelectron spectra (XPS) analysis revealed that Mo deposited on the surface of F8BT was reduced compared to that deposited Mo below the film of F8BT. It is suggested that a chemical interaction between the metal oxide and the organic material affects carrier injection.