Deoxycytidylate (dCMP) deaminase is an enzyme belonged to dCMP cyt deam family. The dCMP deaminase from Streptococcus mutans UA159 was cloned and expressed in E. coli, and purified to homogeneity. The FPLC size exclusion chromatography analysis reveals that the S. mutans dCMP deaminase forms hexamer in solution. The protein was crystallized using hanging drop vapour-diffusion method and diffracted to a resolution of 3.1Å. The diffraction data were collected at BSRF beamline 3W1A. The crystals belong to P2₁3 space group, with unit cell parameters a=b=c=113.2Å, α=β=γ=90°. Assuming there are two subunits per asymmetric unit, the Matthews coefficient is 3.6ų·Da^-1. This is the first crystallization report of the wild-type deoxycytidylate deaminase.