In the biosynthesis of molybdopterin cytosine dinucleotide cofactor, MocA, molybdenum cofactor cytidylyltransferase, transfers the cytosine monophosphate moiety from cytosine triphosphate (CTP) to Mo-molybdopterin. In this study, we heterologously overexpressed MocA from Mycobacterium sp. strain JC1 DSM 3803 and purified the protein by Ni-NTA affinity and size-exclusion chromatography. The MocA protein was incubated with CTP and MnCl₂, then crystallized under conditions containing 10% polyethylene glycol 6000 and 2 M sodium chloride. X-ray diffraction data were acquired at 1.55 Å resolution and belonged to the space group a P4₃2₁2, with unit cell parameters a = 53.965 Å, b = 53.965 Å, c = 130.184 Å, and α = β = γ = 90°. An asymmetric unit of the crystal contains one MocA molecule with solvent content of 45.49% and Mathewes coefficient of 2.26 ų/Da. A high-quality electron density map for the MocA complexed with CTP was obtained by a molecular replacement method.