We have synthesized (8-hydroxy-7-propylquinoline) zinc(II) (Zn(HPQ)(2)) to use in OLED. Photoluminescence (PL) peak of Zn(HPQ)(2) was observed at 555 nm which showed yellow emission. In the cyclic voltammetry (CV) experiment, the HOMO and the LUMO of the Zn(HPQ)(2) measured to be 6.7 eV and 3.3 eV. So we expected that Zn(HPQ)(2) could be used as emitting layer (EML) and electron transporting layer (ETL). In this study, we investigated the efficiency properties of OLED based on Zn(HPQ)(2) as ETL. The device structures were ITO/NPB/Alq(3)/Zn(HPQ)(2)/LiF/Al. Prior to film deposition, ITO substrate performed surface treatment by UV-ozone for 1 minute. We fabricated devices by thickness change of Zn(HPQ)(2), so we founded optimal condition about thickness. Improvement of the OLED performance can be attributed to the reduction of the electron injection barrier of the Zn(HPQ)(2) layer.