Polypropylene wood-plastic composites were prepared with untreated and silane-treated wood flour. They were immersed in water at two different temperatures to investigate the effect of temperature on the water absorption behaviour of selected samples, with 30 wt% untreated and treated wood flour. It was found that the moisture equilibrium for materials containing 30 mass% untreated as well as those with the same content silane-treated wood flour was not reached еven in 360 hours at 25°C. The maximum water absorption at 90°C for compositions based on polypropylene and 30 mass% of untreated and treated fillers was 5.07 and 6.75%, respectively. Tensile tests were conducted on the composite samples before and after immersion and the results were compared with their corresponding dry specimens. After immersion in water treated filler showed an increase in tensile strength and modulus of elasticity, while the untreated wood flour samples, higher relative elongation at break.