Abstract: The invention relates to a method for manufacturing of anionic polycaprolactam with a low content of water extractables and high stability of the degree of polymerization during melting by a two-stage polymerization using known basic initiators and known activators of the following types: ##STR1## where R is ##STR2## R.sup.1 = R or C.sub.1-4 alkyl, cycloalkyl or allyl, R.sup.2 = C.sub.1-4 alkyl or H atom, n is an integer 3-11 and x is an integer >3. The ratio of activator to initiator (e.g. sodium dihydromethoxyethoxyaluminate) ranges between 2.6 and 4.2, advantageously 2.8-3.5 The first polymerization stage proceeds at 150.degree.-200.degree. C. for .ltoreq.10 min, the polymer is then shaped and postpolymerized at 150.degree.-200.degree. C. for .ltoreq.90 min to achieve a monomer content near to the equilibrium content corresponding to the 2nd stage temperature.