The formation of extracellular crystal aggregates of bobierrite (Mg₃(PO₄)₂·8H₂O) by Acinetobacter sp. is found with the use of B-17 medium. The crystal aggregates were observed in the colonies as deposits of brown-yellow coloration, and were identified by X-ray powder diffraction, chemical analysis, infrared spectra and scanning electron microscopy. The production of bobierrite by soil bacteria may imply further versatility of the crystals formation by microorganisms.