Keap1 (Kelch-like ECH-associating protein 1) is a negative regulator of the Nrf2 transcription factor in the cytoplasm. The Kelch/DGR (double-glycine repeat) domain of Keap1 associates with Nrf2 as well as with actin filaments. A recombinant protein containing both the Kelch/DGR domain and the C-terminal region of mouse Keap1 was expressed in Escherichia coli, purified to near-homogeneity and crystallized by the sitting-drop vapour-diffusion method. The crystal belongs to space group P6(1) or P6(5), with unit-cell parameters a = b = 102.95, c = 55.21 A, and contains one molecule in the asymmetric unit. A complete diffraction data was collected to 2.25 A resolution using an R-AXIS IV++ imaging plate mounted on an RA-Micro7 Cu Kalpha rotating-anode X-ray generator.