This work focuses on the comparison of two different thermal conversion processes with respect to different tar amounts and tar compositions at different temperatures and process parameters. Steam gasification experiments were carried out in a 100 kW dual fluidized bed steam gasifier at a temperature range of 700 to 870 degrees C with straw and wood. Pyrolysis experiments were conducted in a rotary kiln reactor at temperatures between 600 and 630 degrees C and straw as fuel. For better understanding of tar formation during thermo-chemical conversion of biomass, the tar content and composition in the product gas were analyzed with a gas chromatograph coupled with a mass spectrometer. The main observation was that at higher temperatures the tar composition is shifted to higher molecular tars such as polyaromatic hydrocarbons (PAN). Key tar components at lower temperatures (pyrolysis) are phenols. The tar content and composition in the product gas of steam gasification of straw and wood as well as the tar yields and composition of low temperature pyrolysis of straw are presented in the following work.