In order to improve the characteristics of sol-gel-derived ZnO thin films synthesized on polyimide (PI) substrates by controlling their degree of bending, we have devised counterpoise-assisted annealing (CAA) in which an external force is applied to the thin films by placing a counterpoise (0, 5, 20, or 50 g) on them. It was found that CAA could suppress the outward bending of the ZnO thin films during the post-annealing process. In addition, the crystallinity, photoluminescence, and electrical properties of the ZnO thin films exhibited significant improvements with an increase in the counterpoise mass to 20 g. Thus, we expect that the CAA method will emerge as an alternative route for synthesizing and optimizing flexible ZnO-based devices. (C) 2015 Elsevier B.V. All rights reserved.