To obtain the subject catalyst consisting of a specific quaternary ammonium organic acid salt, capable of imparting magnetic coating materials with long pot life, excellent curability, magnetic substance dispersability, environmental compatibility, etc., also capable of improving the calenderability and adherability to base film in producing magnetic tapes.

This catalyst consists of (A) a compound of the formula [R1 to R3 are each a 1-11C (branched) (un)saturated hydrocarbon group, and two of them may form, via O or N atom, a heterocycle; R4 is a 1-8C alkyl or aromatic hydrocarbon group; X is an organic acid group] (e.g. methyl triethyl ammonium caprylate). The compound A is prepared, for example, by reaction of a tertiary amine with a carbonic diester to form a quaternary ammonium carbonate followed by subjecting the quaternary ammonium carbonate and an organic acid to anion exchange process.