We have investigated effects of passivation layer on the electrical stability of Indium-Gallium-Zinc-Oxide thin-film transistors with single passivation layer and double passivation layer fabricated on plastic substrate. The positive bias stress and negative bias stress were applied to the IGZO TFTs at various temperatures from 20°C to 80°C. The threshold voltage shift of double passivation device was larger than that of single passivation device under NBTS. The threshold voltage shift of double passivation device was slightly less than that of single passivation device under PBTS. The threshold voltage shift of NBTS is considerably increased than that of PBTS at high temperature due to the difference between conduction band offset and valence band offset.