This invention concerns a process for the polymerization of dodecalactam in the presence of potassium hydroxide or potassium carbonate and water, offering a fast way of obtaining a high yield of polyamides with high molecular weight and with excellent resistance of degradation, and consequently hydrolysis, when kept in contact with boiling water. Polymerization is carried out, preferably at between 290* and 320*C, in the presence of between 0.05 and 2.5% of potassium hydroxide or potassium carbonate. The polymers thus obtained can be readily used to manufacture molded articles, sheets, tubes or pipes, by extrusion, injection or blowing.