Staggered bottom-gate hydrogenated nanocrystalline silicon (nc-Si:H) thin film transistors (TFTs) fabricated on flexible transparent polyimide substrates were investigated. The saturation electron field-effect mobility and electrical bias-stress stability of these TFTs were evaluated under applied tensile mechanical strain parallel to the source-drain direction. The mobilities increased accompanying with deteriorated electrical stabilities as the applied tensile strain increased. The power-law dependence between threshold voltage shift and gate-bias stressing time indicates that the instability is mainly caused by the state creation at the interface between nc-Si:H channel and gate dielectric.