The electronic properties of five derivatives of bis[2-(2-hydroxyphenyl)benzoxazolate] zinc (ZnPBO) have been investigated by the time-of-flight measurement of their thin films prepared with vacuum deposition. The electron and hole mobilities at electric field of 5 x 10(5) V/cm for these compounds were 10(-5) cm(2) /Vs and 10(-6)-10(-8) cm(2) /Vs, respectively. The electron mobility was found to be almost identical among those used in this study and higher than that of the representative electron transporting organic material, Alq. The hole mobility had significantly increased as the pi-conjugation of the ligands of the complexes was extended.