Abstract: Novel guanidated aminophosphonic acid compounds their use as biocides and their intermediates. The compounds are guanidated N-(aminoalkyl) aminoalkanephosphonic acid derivatives and are characterized in that they comprise both a phosphonic acid type group and at least one guanidino group and also in that they are based on alkylene amines. The compounds have the general formula: ##STR1## wherein Z and Z' are hydrogen, a lower alkyl group or an alkali metal, Y is hydrogen or an amidine group, m is 1-3, n is 4-16 and p is 1-3. The compounds can be prepared by reacting a halogenoalkanephosphonic acid compound with an alkylene di- or polyamine followed by guanidation of the so obtained product. The compounds are particularly useful as fungicides and especially as fungicides for industrial purposes.