Even when used in applications such as electronic materials, display materials, and inks, in which required standards in terms of coloring prevention, long term stability, low impurity content, and the like, are extremely high, the present invention can meet such required standards. The present invention addresses the problem of providing an allylamine (co)polymer which overcomes the limitations of the prior art, undergoes little coloring, contains little impurities and exhibits excellent long term stability; and a method for producing the same. This problem can be solved by an allylamine (co)polymer which has constituent units derived from allylamine and contains sulfuric acid groups in the structure thereof, in which the proportion of the sulfuric acid groups with respect to the total mass of the allylamine (co)polymer is 20,000 ppm by mass or less.