A powder derivative of acid pre-hydrolysis processing of cellulosic wastes, known as cellulignin, was used as filler in resin matrix composites. The flexural mechanical properties of cellulignin-polyester, epoxy or urea-formaldehyde matrix composites was evaluated. The results obtained show that the urea-formaldehyde and epoxy based composites can be used as alternative materials for low cost and low strength applications. Their advantages over the common wooden agglomerates or composites are presented and are based on the fact that cellulignin can be obtained virtually from any cellulosic waste.