In this study, we investigated the effect of electrode materials on the electrical characteristics of coplanar top-gate a-ITGZO thin-film transistors, in which the gate, source, and drain electrodes were made of the same metal, Ti or Al. The field-effect mobilities of the a-ITGZO thin-film transistors with Ti and Al electrodes were 35.2 and 20.1 cm²/V·s, respectively, and the threshold voltage of the a-ITGZO thin-film transistor with Ti electrodes was -0.4 V, whereas that of the transistor with Al electrodes was -1.8; this shift is attributed to the fact that Ti has a higher work function than Al. When Ti was used as the source and drain electrode material, the channel resistance and effective channel length were reduced owing to the penetration of metal atoms into the channel region from the edge of the source/drain electrodes.