There is a variety of metalloenzymes in the biological system. The organisms use them to maintain their life. Herein, we introduce a special enzyme: Cysteine Dioxygenase (CDO); CDO is a non-heme iron enzyme, which can convert cysteine (Cys) into cysteine sulfinic acid (CSA). This conversion plays an important role in cysteine catabolism in mammalian tissue. Deficiency of CDO has been correlated with Alzheimer’s, Parkinson’s and other neurological disorders. Structural comparison from the typical non-hemeFe(II) dioxygenases to CDO, the coordination sphere of the Fe in CDO deviates fromthe fac-2-Histeines-1-carboxylate to a 3-Histeines facial triad. Themechanistic information of CDO, involves in O2 activation to generate Fe(III)-O2 − or further leading to the formation of Fe(IV) = O species, is still not clear. Biomimetic studies suggest the S-oxygenation mediatedby an Fe(II)-SR complex and O2 is expectable.