Combustion of biomass under fixed-bed conditions will generate both coarse and fine particles that have a negative effect on technical performance or pose health hazards. It is therefore important to reduce the emissions of these particles that are already in the combustion process. The aim of this study was to experimentally investigate how different air supply strategies affect the particle emission in fixed-bed combustion of biomass. The air was supplied either through the grate, through a secondary air register, or equally divided between the two. The results showed that the air supply affects the emissions of both coarse and especially fine fly ash particles. The emissions of fine particles decrease when the air supply through the grate decreases, probably due to lower oxygen concentration in the fuel bed and thereby lower temperature in the burning char particles, which results in less vaporisation of ash elements. Hence, changing or optimizing the air supply strategy appears to be an attractive way to reduce the particle emissions already in the combustion process.