The ectoine hydroxylase (EctD) is a member of the non-haem-containing iron(II)- and 2-oxoglutarate-dependent dioxygenase superfamily. Its mononuclear iron centre is a prerequisite for the activity of this enzyme and promotes the O₂-dependent oxidative decarboxylation of 2-oxoglutarate, which is coupled to a two-electron oxidation of the substrate ectoine to yield 5-hydroxyectoine. An expression and purification protocol for the EctD enzyme fromSphingopyxis alaskensiswas developed and the protein was crystallized using the sitting-drop vapour-diffusion method. This resulted in two different crystal forms, representing the apo and iron-bound forms of the enzyme.