Acetate kinase (AckA) catalyzes the reversible transfer of a phosphate group from acetyl phosphate to ADP, generating acetate and ATP, and plays a central role in carbon metabolism. In the present work, the gene corresponding to AckA from Salmonella typhimurium (StAckA) was cloned in the IPTG‐inducible pRSET C vector, resulting in the attachment of a hexahistidine tag to the N‐terminus of the expressed enzyme. The recombinant protein was overexpressed, purified and crystallized in two different crystal forms using the microbatch‐under‐oil method. Form I crystals diffracted to 2.70 Å resolution when examined using X‐rays from a rotating‐anode X‐ray generator and belonged to the monoclinic space group C2, with unit‐cell parameters a = 283.16, b = 62.17, c = 91.69 Å, β = 93.57°. Form II crystals, which diffracted to a higher resolution of 2.35 Å on the rotating‐anode X‐ray generator and to 1.90 Å on beamline BM14 of the ESRF, Grenoble, also belonged to space group C2 but with smaller unit‐cell parameters (a = 151.01, b = 78.50, c = 97.48 Å, β = 116.37°). Calculation of Matthews coefficients for the two crystal forms suggested the presence of four and two protomers of StAckA in the asymmetric units of forms I and II, respectively. Initial phases for the form I diffraction data were obtained by molecular replacement using the coordinates of Thermotoga maritima AckA (TmAckA) as the search model. The form II structure was phased using a monomer of form I as the phasing model. Inspection of the initial electron‐density maps suggests dramatic conformational differences between residues 230 and 300 of the two crystal forms and warrants further investigation.