In this study, the overexpression, purification and crystallization of selenomethionine (SeMet) incorporated glycinamide ribonucleotide synthetase (GAR-syn) from Escherichia coli are reported. The overexpression of SeMet GAR-syn was placed under the control of the isopropylthio-beta-galactoside (IPTG) inducible T7 RNA-polymerase system. The newly developed construct contained a removable histidine tag on the amino terminus of GAR-syn, which allowed rapid purification using metal-chelate chromatography techniques. The SeMet GAR-syn crystals were grown by hanging-drop vapor diffusion and belong to the space group P212121 with unit-cell parameters a = 56.2, b = 62.4 and c = 129.8 A and a single monomer in the asymmetric unit. The crystals diffract to 1.6 A resolution and have led to the determination of multiple-wavelength anomalous diffraction phases to 2.2 A resolution.