Thin-film transistors (TFTs) with a ZrZnSnO (ZZTO) channel layer were fabricated using a solution process. As-prepared ZnSnO (ZTO) TFTs had a large off-current. However, as the content of Zr ions increased in ZTO, the threshold voltage shifted, and the off-current in the TFTs decreased. Because Zr has a lower standard electrode potential, it is more readily oxidized than Sn or Zn. Thus, Zr acted as an effective carrier suppressor in the ZTO system and a ZZTO TFT with a high mobility of a 4.02 cm2 V−1 s−1 and a large on/off ratio of over 106 was achieved.