Oxidoreductases are classified as EC 1 in the EC number classification of enzymes. Oxidoreductases can be further classified into 21 subclasses:
* EC 1.1 includes oxidoreductases that act on the CH-OH group of donors (alcohol oxidoreductases such as methanol dehydrogenase)
* EC 1.2 includes oxidoreductases that act on the aldehyde or oxo group of donors
* EC 1.3 includes oxidoreductases that act on the CH-CH group of donors (CH-CH oxidoreductases)
* EC 1.4 includes oxidoreductases that act on the CH-NH group of donors (Amino acid oxidoreductases, Monoamine oxidase)
* EC 1.5 includes oxidoreductases that act on CH-NH group of donors
* EC 1.6 includes oxidoreductases that act on NADH or NADPH
* EC 1.7 includes oxidoreductases that act on other nitrogenous compounds as donors
* EC 1.8 includes oxidoreductases that act on a sulfur group of donors
* EC 1.9 includes oxidoreductases that act on a heme group of donors
* EC 1.10 includes oxidoreductases that act on diphenols and related substances as donors
* EC 1.11 includes oxidoreductases that act on peroxide as an acceptor (peroxidases)
* EC 1.12 includes oxidoreductases that act on hydrogen as donors
* EC 1.13 includes oxidoreductases that act on single donors with incorporation of molecular oxygen (oxygenases)
* EC 1.14 includes oxidoreductases that act on paired donors with incorporation of molecular oxygen
* EC 1.15 includes oxidoreductases that act on superoxide radicals as acceptors
* EC 1.16 includes oxidoreductases that oxidize metal ions
* EC 1.17 includes oxidoreductases that act on CH or CH groups
* EC 1.18 includes oxidoreductases that act on iron-sulfur proteins as donors
* EC 1.19 includes oxidoreductases that act on reduced flavodoxin as a donor
* EC 1.20 includes oxidoreductases that act on phosphorus or arsenic in donors
* EC 1.21 includes oxidoreductases that act on X-H and Y-H to form an X-Y bond