To obtain dimethylcyclooctane dimethanol useful as a material or additive for synthetic resins as polyester, polyurethane and nylon, synthetic fibers, lubricants, plasticizers.

This dimethylcyclooctane dimethanol of formula I (one of R1 and R2 is methyl, and the other is hydroxymethyl), e.g. 2,6-dimethyl-1,5- cyclooctane dimethanol and/or 2,5-dimethyl-1,6-cyclooctane dimethanol, is obtained by hydrogenating a dimethylcyclooctane dicarboaldehyde of formula II (e.g. 2,6-dimethyl-1,5-cyclooctane dicarboaldehyde and/or 2,5-dimethyl-1,6- cyclooctane dicarboaldehyde) in the presence of a catalyst (e.g. Raney nickel) under pressure of 1-150atm. at 60-140°C. The addition of the catalyst to this reaction system (liquid-phase suspension type) is preferably 0.5-5wt.% in conversion to metal atoms to the quantity of the reaction mixture.