A heat-curable, cathodically depositable aqueous electrocoating composition contains(A) from 50 to 95% by weight of a polymerization or polycondensation or polyaddition product which has an average molecular weight of from 200 to 20,000 and primary and/or secondary hydroxyl groups and primary, secondary and/or tertiary amino groups and is water-thinnable on protonation with an acid, and(B) from 5 to 50% by weight of a water-thinnable crosslinking agent having cationic groups or groups which are convertible into cationic groups by protonation with an acid.