A systematic investigation of the determination of humic acid charge density has been carried using cationic copolymers of different molecular mass and charge density and polydiallyldimethylammonium chloride(PDDA) using three different techniques of end point determination(spectrophotometry, color removal method and photometric dospersion analyzer(PDA) method). The charge density values of humic acid obtained for each of the polymers from different techniques are consistent but depend on the charge density of the polymers used. When lower charge polymers are used, lower charge density values of humic acid are obtained, but for polymers of high charge density(above 2.5 meq/g), the measured charge density values of humic acid are almost identical. The latter values are nearly the same as those obtained for PDDA which has a very high charge density(above 6 meq/g). For polymers of lower charge density, it is considered that the optimum dosage does not correspond to 1:1 charge neutralization between anionic and cationic groups. Polymers of high charge density(above 2.5 meq/g) should be used in order to achieve a complete charge neutralization.