Previously, we reported that the iridium complexes, Ir(2,3-dpqx-F-2)(2)(acac) and Ir(2,3-dpqx-F-2)(2)(przl-CH3), exhibited electroluminescence (EL) emission at 630 and 641 nm with luminous efficiencies of 4.18 and 3.46 cd/A, respectively. 2,3-dpqx-F-2, acac and przl represent the anions of 2,3-bis-(4-fluorophenyl)quinoxaline, acetylacetone and 4-acetyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one, respectively. In this study, several pyrazolone-based ligands, 4-R-5-methyl-2-pherryl-2,4-dihydro-pyrazol-3-one (przl-R) series, where R represents either p-tolyl or p-chlorophenyl, were prepared and introduced to the iridium complexes as new ancillary ligand substitutes for acac. The purpose of this study was to find the effects of the ancillary ligand on the emission color and the luminous efficiencies of the iridium complexes. Thus, we investigated the luminescence properties of the iridium complexes and compared them with luminous efficiencies of Ir(2,3-dpqx-F-2)(2)(acac) and Ir(2,3-dpqx-F-2)(2)(przl series). The photoluminescence maxima of Ir(2,3-dpqx-F-2)(2)(przl series) were observed around 630 nm, similar to that of Ir(2,3-dpqx-F-2)(2)(acac) at 631 urn. On the other hand, the electroluminescence of the complexes containing a przl ligand exhibited a bathochromic shift from that of the analog containing acac, as expected. The luminance efficiencies were also improved upon involvement of bulky substituents.