Abstract The revolutionary transformation of opaque wood into a transparent material, with combination of high optical transmittance and high haze, has gained widespread interest in the realms of advanced functional materials. However, the thickness of transparent wood composite (TWC) is limited to a few millimeters which restricts potential use. In this study, TWC were prepared using transverse sections of poplar (Populus deltoides) in thickness ranging from 1.5 to 15 mm by lignin modification bleaching followed by epoxy resin infiltration. The effects of bleaching duration as well as sample thickness on the optical properties of TWC were investigated. TWC was characterized using scanning electron microscopy and FTIR spectroscopy. The optical properties of TWC were measured using UV-VIS-NIR spectroscopy. The results indicated that light transmittance depended on severity of bleaching, lignin content and sample thickness.