A process for the production of low-molecular-weight allylamine polymer having a weight average molecular weight of 250 to 4,000 or an addition salt thereof, which comprises neutralizing with an alkali a polymerization solution containing said low-molecular-weight allylamine polymer to bring said allylamine polymer into a free state, then distilling said low-molecular-weight allylamine polymer solution containing an unreacted monoallylamine and a salt, thereby distilling off the unreacted monoallylamine, then, subjecting the residue to electrodialysis, and optionally carrying out acid treatment.