To provide a method of manufacturing a polymer containing an oxazoline group, small in the performance change even in the long period storage of the polymer containing an oxazoline group, that is, to provide the method of manufacturing a stabilized polymer containing an oxazoline group.

A method of manufacturing a stabilized polymer containing an oxazoline group is carried out by mixing an aqueous solvent solution of the polymer containing an oxazoline group with an alkaline aqueous solution and adjusting the aqueous solvent solution to pH of 8-11.