We investigated processing temperature dependencies of the preferred orientation axis of REBa/sub 2/Cu/sub 3/O/sub 7-y/ (RE123; RE=Yb, Er, Y, Gd, Sm, Nd, Pr and La) films prepared on various substrates by chemical solution deposition (CSD) using metal naphthenates. In the case of RE=Er, Y, Gd and Sm prepared on SrTiO/sub 3/, a/b-axis oriented films were obtained in a region of low temperatures, whereas there is no such temperature region for RE=Yb, Nd, Pr and La films. On the other hand, RE123 films prepared on LaAlO/sub 3/ gives a/b-axis orientation in a region of low temperatures except for Yb123 film. The (102) pole figures of these films give four high density points with four-fold symmetry, indicating that their axes are in-plane aligned. In order to confirm relationship between a/b-axis oriented growth and ionic radius of RE elements (R/sub i,RE/), we prepared rare-earth mixed Yb/sub 1-x/Er/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-y/ and Sm/sub 1-x/Nd/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-y/ films. Orientation of these films changed critically at certain average R/sub i,RE/'s.