The goal of this study is to investigate the applicability of asymmetrical flow field-flow fractionation (AsFlFFF)-multi angle laser light scattering (MALLS), and to develop a method for analysis of cationic potato amylopectin (CPAP) having ultrahigh molecular mass (UHMr). Use of the aqueous carrier having low salt content (3 mM NaN3) resulted in a distortion in AsFlFFF fractograms of CPAP with a general pattern of a sharp rise at the beginning of the elution followed by a long tailing, probably due to combination of attractive and repulsive charge interactions (attractive interaction between CPAP molecules and the channel membrane, and repulsion among cationic CPAP molecules). As the cross flow-rate (Fc) increases, the tailing tends to increase, and the repeatability of the AsFlFFF retention data tends to decrease, which is an indication of the presence of the charge interactions. The tailing gradually decreased, and the repeatability of the AsFIFFF retention data increased, as the salt content of the carrier increased. The distortion of the fractogram finally disappeared at Fc of about 0.2 ml/min and the channel flow-rate (F(out)) of about 1 ml/min with the aqueous carrier having the salt content of 40 mM (3 mM NaN3 +37 mM NaNO3). The weight-average molecular mass (Mw) and the z-average radius of gyration ((rg),) determined by MALLS were 5.2 x 10(7) and 34 x 10(1) nm, respectively. With the flow-rate ratio, Fc/F(out) kept constant, the degree of the charge interactions (and thus the distortion of fractogram) seems to increase with the cross flow-rate (Fc) and with the sample injection mass. AsFIFFF-MALLS was applied for determination of molecular mass distributions (MrDs) and the sizes of CPAPs prepared by various cooking procedures.