Co-gasification tests were carried out with wood pellets and lignite at lignite ratios ranging from 0 to 100% in the dual fluidized bed pilot plant at Vienna University of Technology. The operating parameters for all gasification and co-gasification tests were kept constant; the input fuel power was chosen as 90 kW(th) while the gasification temperature was held at 850 degrees C. Olivine was used as the bed material. In addition to standard online measurements of the permanent gas components of the product gas, the tar content was also measured. NH3 and H2S were detected in the product gas for gasification of the pure fuels. It turned out that increasing lignite ratios in the fuel mix with biomass improved the quality in terms of reducing tar load and the possibility to adjust the main components of the product gas. The beneficial effects of lignite can be reached already at low proportions of lignite in the fuel mix with wood which will be presented in this paper.