Hydrogen-incorporated amorphous In-Sn-O (a-ITO) thin films were fabricated by introducing hydrogen gas during deposition. The hydrogen concentration in the thin films was experimentally determined to vary from 4.7 x 10(20) to 8.1 x 10(20) cm(-3) with increasing H-2 flow rate. The mechanical stability of the a-ITO thin films dramatically improved with the optimal amount of hydrogen (similar to 5.3 x 10(20) cm(-3)), without any observable degradation in electrical or optical properties. With increasing hydrogen concentration to the optimal value, the compressive residual stress gradually decreased and the subgap absorption at similar to 3.1 eV was suppressed. Considering that the residual stress and subgap absorption mainly originate from defects, hydrogen may be a promising candidate for defect passivation in flexible electronics.