The aim of this study was to investigate the influence and performance of the addition of support material on the phosphate uptake in a pure culture of phosphate-accumulating bacteria Acinetobacter calcoaceticus (DSM, 1532). Materials (natural zeolite and clay from Hrvatsko zagorje, Croatia) of different physical, chemical and mineral characteristics as well as different particle size were tested. In anaerobic/aerobic sequencing batch reactors with the pure culture of A. calcoaceticus, the addition of natural zeolite or clay in the aerobic phase resulted in a significantly higher final efficiency of phosphate removal. The amount of phosphate removed depended on particle size and type of material used. The number of A. calcoaceticus cells was significantly higher in reactors with support materials than in control reactors. After 24 h of incubation with support materials, the cells were present in colonies on the outer layer, strongly adsorbed and adhering to one another by extracellular substances. The main contribution of the support material to the phosphate removal was the increase of biomass, and in a lesser extent the adsorption of phosphate on the material particles.