The PTB domain of mouse dok1 fusion protein has been overexpressed in Escherichia coli and crystallized in a form suitable for X-ray crystallographic study. Crystals have been obtained using the vapour-diffusion method and belong to space group P2(1)2(1)2(1). X-ray diffraction data were collected in-house to 2.5 A resolution. A selenomethionine (SeMet) dok1 PTB fusion-protein derivative was expressed using the same expression system, purified in a reductive environment and crystals were obtained under similar conditions. Subsequently, three different wavelength data sets from the derivative crystal were collected to 2.5 A resolution at SPring-8.