Polyhydroxyalkanoates are linear polyesters that are produced by bacterial fermentation and are used as biodegradable bioplastics. β‐Ketothiolase B (BktB) from Ralstonia eutropha (ReBktB) is a key enzyme for the production of various types of copolymers by catalyzing the condensation reactions of acetyl‐CoA with propionyl‐CoA and butyryl‐CoA. The ReBktB protein was crystallized using the hanging‐drop vapour‐diffusion method in the presence of 25% polyethylene glycol 3350, 0.1 M bis‐tris pH 6.5, 0.2 M lithium sulfate at 295 K. X‐ray diffraction data were collected to a maximum resolution of 2.3 Å on a synchrotron beamline. The crystal belonged to space group C2221, with unit‐cell parameters a = 106.95, b = 107.24, c = 144.14 Å. With two molecules per asymmetric unit, the crystal volume per unit protein weight (VM) is 2.54 Å3 Da−1, which corresponds to a solvent content of approximately 51.5%. The structure was solved by the molecular‐replacement method and refinement of the structure is in progress.