AbstractResearch on mixed forests has mostly focused on tree growth and productivity, or resistance and resilience in changing climate conditions, but only rarely on the effects of tree species mixing on timber quality. In particular, it is still unclear whether the numerous positive effects of mixed forests on productivity and stability come at the expense of timber quality. In this study, we used photographs of sawn boards from 90 European beech (Fagus sylvaticaL.) trees of mixed and pure forest stands to analyze internal timber quality through the quality indicatorknot surfacethat was quantitatively assessed using the software Datinf® Measure. We observed a decrease inknot surfacewith increasing distance from the pith as well as smaller values in the lower log sections. Regarding the influence of neighborhood species identity, we found only minor effects meaning that timber qualities in mixed stands of beech and Norway spruce (Picea abies(L.) H. Karst.) tended to be slightly worse compared to pure beech stands.