In the years 1999-2001 occurrence of eriophyoid mites (Eriophyoidea) and spider mites (Tetranychidae) on wild grasses growing in Wielkopolska region was investigated. Seven species of eriophyoid mites and three of spider mites were found on 24 grass species. Eriophyoid mites infested 38% and spider mites 57% of all examined samples. The most frequent inhabited grass species by eriophyoid mites were Agropyron repens and Lolium perenne, while by spider mites Dactylis glomerata and Bromus mollis.