Dolomite is considered advantageous as bed material in fluidized bed gasification processes, due to its catalytic tar cracking and anti-sintering properties. However, in case of pressurized fluidized bed gasifiers, the use of dolomite is challenging. High temperature in the presence of steam favors the production of clean syngas due to the intensified cracking of tar in the presence of CaO, whereas it simultaneously increases the tendency of fragmentation of dolomite particles after full calcination. The present study was carried out to examine the influence of the properties of dolomite on the stability of dolomite in a pressurized fluidized bed gasifier, with the aim of determining criteria for dolomite selection. Glanshanunar dolomite exhibited a better stability in the mechanical strength after calcination, compared to Sala dolomite. The corresponding change of micro-structure that occurred during dolomite chemical transformation was presented. The crystal pattern and Si distribution in the crystal lattice are the possible explanations for the superior performance of the Glanshammar dolomite compared to the Sala dolomite.