Wood plastic composite (WPC) is an important representative of the group of natural fibre reinforced plastics. In order to bond the polar wood fibres chemically to the nonpolar polymer matrix, coupling agents are used. The most important group of coupling agents for WPC are maleated polyolefins in which the backbone polymer as well as the maleic anhydride content (MAH-content) can be varied. In this study, the influence of the flowability and the MAH-content of coupling agents on rheological and mechanical interaction effects of wood fillers in different WPC formulations have been investigated. It has been shown that the MAH-content as well as the flowability of coupling agents is in terms of rheological interaction effects of negligible influence. Furthermore, it was found that mechanical interactions are significantly influenced by coupling agents. In this context, the flowability of the coupling agent is of greater importance than the MAH-content.