Silicon-on-insulator (SOl) technology is being investigated for monolithic pixel device fabrication. The SOl wafers by UNIBOND allow the silicon resistivity to be optimized separately for the electronics and detector parts. We have fabricated pixel detectors using fully depleted SOl (FD-SOI) technology provided by OKI Semiconductor Co. Ltd. The first pixel devices consisting of 32×32 pixels each with 20 pm square were irradiated with 60CO γ's up to 0.60 MGy and with 70-MeV protons up to 1.3×1016 I-MeV neqcm2. The performance characterization was made on the electronics part and as a general detector from the response to RESET signals and to laser. The electronics operation was affected by radiation-induced charge accumulation in the oxide layers. Detailed evaluation using transistor test structures was separately carried out with covering a wider range of radiation level (0.12 kGy to 5.1 MGy) with 60CO γ's.