A measurement of total-dose radiation effects of SOI-MOS transistors is presented. The motivation of this study is to understand radiation effects of a single transistor, which is fabricated with the same structure (BESOI) as a preamplifier planned to be used for the silicon vertex detector in the KEK BELLE experiment. Results are given with the threshold voltage shift (ΔV th), mobility degradation and increase of the 1/f noise. We decomposed ΔVth into the oxide trap and interface trap components. Using this decomposition result, we found good agreement of data for the mobility degradation versus interface traps and the 1/f noise increase versus oxide trapped charges with the empirical relations.