Acyl carrier protein synthase (AcpS) catalyzes the transfer of 4'-phophopantetheine from coenzyme A to the acyl carrier protein (ACP) to activate it for fatty-acid biosynthesis. Two crystal forms of Staphylococcus aureus AcpS have been generated at 277 K using either NaCl or PEG 6000 as a precipitant. The diffraction patterns of the crystals extend to 1.65 and 1.8 A, respectively. Full sets of X-ray diffraction data were collected from native crystals and the crystal structures were solved by molecular replacement.