Before injection molding, wood polymer composites (WPC) normally have to be dried to achieve optimal quality of the injected parts as well as to avoid corrosion of the mold. Based on a literature study, there are currently no published investigations dealing with the dependency of WPC properties on the initial moisture content of the compound's pellets. Further, it is known that water and wood in combination with high temperatures can lead to corrosion of steel parts, but a systematic analysis of the impact of WPC injection molding on tool corrosion has not been found in the literature. For the present study, a compound with 68 wt% (weight percent) polypropylene, 30 wt% wood flour and 2 wt% coupling agent was produced and tested in injection molding trials. Specimens according to ISO 527-2 were produced from WPC with defined moisture contents, respectively. Compound moisture, already at very low contents, had significant negative effects on the tested mechanical properties, namely tensile modulus and strength, unnotched and notched Charpy impact strength and heat deflection temperature. Corrosion trials were performed for different tool steel qualities. The severity of corrosion correlates with the amount of chromium (Cr) in the alloys tested.