We investigated the stability of a-Si:H TFTs under mechanical strain with and without silicon nitride (SiNx;H) passivation. The process temperature of these flexibledevice, including the passivation layer, was well-controlled below 200°C, and the substrate was using stainless steel foil. The strain stress was applied cylindrically parallel to the active channel path of TFTs. The stability measurement was performed by DC gate bias stress and lasted up to 10 4 seconds, By using electrical parameter fitting, the V th, metastability mechanism was dominated by state creation effect. Our result indicated the device with passivation layer was improved, and the V th had less variation under both outward and inward bending. By exerting 190°C post-annealing process after SiNx:H deposited, the V th was shifted left and the reliability of flexible TFTs became better than without post-annealing process. That's related to the passivating effect of hydrogen ion under passivation layer and post-annealing process.