Effects of alkalization, esterification, and ?-irradiation of wood on the transcrystalline morphology of wood/polypropylene composites were investigated using X-ray diffraction, hot stage optical microscopy, and scanning electron microscopy. The occurrence of transcrystallization in wood-polypropylene composites is strongly dependent on the type of chemical modification of lignocellulosic materials. A detailed analysis of the results obtained proved that the transcrystallization is strongly influenced by conditions of mercerization process of wood and kind of anhydrides. Moreover, it has been found that amount of cellulose in wood plays a key role in the development of transcrystallinity. The absence of cellulose in wood seems to be unfavorable for the growth of transcrystallinity. A relationship between mechanical properties of composites and the phenomena taking place at the polymer-filler interface, controlled by chemical modifications of lignocellulose components has been evaluated. It has been established that the mechanical properties of wood composites depend on the proper choice of a modifier and are obtained after optimization of the process of modification. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013