6-Aminocaproic acid is prepared by(a) reacting a 5-formylvaleric acid ester with water in the presence of an acid agent at 30.degree.-200.degree. C. and(b) reacting the 5-formylvaleric acid thus obtained with excess ammonia and hydrogen in the presence of a hydrogenation catalyst and of a solvent which is inert under the reaction conditions at 50.degree.-150.degree. C. under superatmospheric pressure.