In this study, three commercial transition metal oxides such as molybdenum trioxide (MoO3), tungsten trioxide (WO3), and vanadium pent-oxide (V2O5) were employed as hole-injection layer to improve the electrical and optical performance of organic light-emitting diodes (OLEDs). The layer thickness of MoO3, WO3 and V2O5 were respectively varied by 1, 2, 5 and 10 nm inside blue OLED to characterize their effects on device performance. The optimal OLED with a 5 nm MoO3 hole-injection layer performs an enhancement of 12.9% in current efficiency, 17.5% in power efficiency and 9.3% in maximum external quantum efficiency, comparing to that of reference device without hole-injection layer.