We have investigated the effect of the ambient gases on the characteristics of AZO thin films for the OLED (organic light emitting diodes) devices. These AZO thin films are deposited by rf-magnetron sputtering under different ambient gases (Ar, Ar+$O_2$, and Ar+$H_2$) at 300. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0.2sccm to 1sccm and from 0.5sccm to 5sccm, respectively. The AZO thin films were preferred oriented to (002) direction regardless of ambient gases. The electrical resistivity of AZO film increased with increasing flow rate of $O_2$ under Ar+$O_2$ while under Ar+$H_2$ atmosphere the electrical resistivity showed minimum value near 1sccm of $H_2$. All the films showed the average transmittance over 80% in the visible range. The OLED device was fabricated with different AZO substrates made by configuration of AZO/$acute{a}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of AZO substrate.