Highly transparent and multifunctional ZnO/poly(n-butyl methacrylate) (ZnO/PBMA) nanohybrid films with superhigh contents of ZnO nanoparticles (NPs) were synthesized by a bulk polymerization method. The structure; morphology; and optical, mechanical, and thermal properties of the obtained nanohybrid films were studied. ZnO NPs were dispersed uniformly and retained their original size (4-6 nm) in the PBMA matrix without any aggregation. The ZnO/PBMA nanohybrid films allowed more than 90% of visible light at 550 nm to pass and maintained almost the same high transparency as pure PBMA film even when the ZnO NP content was as high as 60 wt %. The nanohybrid films embedded with ZnO NPs exhibited significantly enhanced multifunctional performance, including excellent UV-shielding properties, good thermal stability, high surface hardness, and desired flexibility. In particular, the coefficient of thermal expansion (CTE) of the nanohybrid films clearly decreased to 193 from 325 ppm/K for pure PBMA below the glass transition temperature (T-g) and strikingly decreased from 5378 to 1373 ppm/K after the glass transition. The ZnO/polymer nanohybrids synthesized in this work are promising for the fabrication of optical devices with high transparency, such as flexible displays, optical filters, and flexible solar cells.