Carbon molecular sieves (CMS) for air separation have been prepared from walnut shells. Walnut shells were first carbonized to produce a microporous char. The char was finely ground and extruded with coal tar and phenol-formaldehyde resin (PF resin) as binder. The extrudate was then heat treated to produce a CMS having good air separation ability. Conditions including carbonization temperature, heat treatment temperature, and amounts of coal tar and PF resin were investigated. The micropore structure of the CMS was investigated by means of gas adsorption. The predominating micropore size distribution of the CMS is 3, 3-4. 0 Å.