DREP4 is a nuclease from fruit fly that is involved in apoptotic DNA fragmentation. DREP4 contains a conserved CIDE domain that acts as a protein-interaction module and is critical for its function. In this study, it was found that DREP4 CIDE domains form filament-like structures in solution. The length of the highly ordered filament-like structure is dependent on the salt concentration. By adjusting the salt concentration the DREP4 CIDE domain could be crystallized, and X-ray diffraction data were collected to a resolution of 1.9 Å. The crystals were found to belong to the orthorhombic space group P212121, with unit-cell parameters a = 53.08, b = 76.58, c = 174.59 Å.