Dipeptidyl aminopeptidase IV (DAP IV or DPP IV) from<italic>Pseudoxanthomonas mexicana</italic>WO24 (PmDAP IV) preferentially cleaves substrate peptides with Pro or Ala at the P1 position [NH₂-P2-P1(Pro/Ala)-P1′-P2′…]. For crystallographic studies, the periplasmic form of PmDAP IV was overproduced in<italic>Escherichia coli</italic>, purified and crystallized in complex with the tripeptide Lys-Pro-Tyr using the hanging-drop vapour-diffusion method. Kinetic parameters of the purified enzyme against a synthetic substrate were also determined. X-ray diffraction data to 1.90 Å resolution were collected from a triclinic crystal form belonging to space group<italic>P</italic>1, with unit-cell parameters<italic>a</italic>= 88.66,<italic>b</italic>= 104.49,<italic>c</italic> = 112.84 Å, α = 67.42, β = 68.83, γ = 65.46°. Initial phases were determined by the molecular-replacement method using<italic>Stenotrophomonas maltophilia</italic>DPP IV (PDB entry 2ecf) as a template and refinement of the structure is in progress.