Stoker fired boilers have been used widely for small scale power plant in isolated region or small island in Indonesia and for industries. Nevertheless, stoker fired boilers face some operational problems related to burning low rank coal. Water cooled vibrating grate stoker has potential to minimize the problem compared to traveling grate stoker. In this study, 15 kW (th) vibrating grate stoker simulator has been developed for characterizing combustion in stoker fired boiler. Combustion characteristic such as burning out time and combustion rate can be evaluated for both fixed grate and vibrating grate types. Experimental results plotted in horizontal temperature profiles indicate important combustion steps, i.e. drying, volatile release and char burning. Peak temperature while burning sub-bituminous coal was 861°C, higher than lignite coal of 647°C. In vibrating grate, the combustion rate of sub-bituminous and lignite coal in vibrating grate increase 56.5% and 25.9%, respectively, compared with in fixed grate. Application of vibrating grate instead of fixed grate in boiler can minimize the furnace size room because of higher heat release rate per area.