Biomass steam gasification is a promising way of producing synthetic gas that can be used for example in chemical industry and for fuel production. It can also be combined with heat and power generation and has a high potential as a renewable energy source. This has led to a lot of research about how catalytic active bed material could improve the quality of synthetic gas. Previous publications have shown that catalytic active bed material also has a positive effect on the efficiency of the char gasification reaction by transferring potassium from the bed material to the solid fuel. The present work investigates the impact of different bed materials on steam gasification of char. This should help to analyse the role of alkali metals, especially of potassium, in char gasification. To examine this, a new fluidized bed system on lab scale has been designed and constructed, which allows for the execution of steam gasification experiments without the risk of an interaction between the reactor and the catalytic material. This has been done by performing steam gasification experiments of char in active and nonactive olivine as bed material. After 50% conversion, the char has been analysed with a SEM/EDX. It was found that the activated olivine has a strong catalytic effect on the steam gasification of char. This results in a higher reaction rate a nd a reduction by 50% of the conversion time. Further experiments have shown that this effect is decreasing over time. The char analysis has shown that the potassium was transferred from the bed material to the fuel.