The effects of tannic acid and Rhodamine B on the zeta potentials and surface free energy components of polyester fabric (Dacron 54, Style 777) were studied, Knowledge of these parameters may be helpful in improving the dyeing process of the polyester fabric, It was found that the zeta potential of the fabric in tannic acid solutions (10(-6)-10(-2) M) was negative and its absolute value decreased with increasing concentration of the acid, It was concluded that H+ ions from the tannic acid adsorbed on the polyester surface caused a decrease in the negative zeta potential, The adsorption of tannic acid probably occurs via hydrogen bonding between the hydroxyl phenolic groups of the acid and the carboxyl end-groups of the polyester, which hydrolyze in the acidic medium, The free energy components determined show that the untreated polyester surface is practically monopolar basic with the electron donor component, gamma(s)(-), equal to 56.7 mJ/m(2). This relatively high value probably results from the presence of highly polar carboxyl end-groups, The adsorbed tannic acid causes an increase in the gamma(s)(-) component to 66.4 mJ/m(2) due to the presence of more polar groups on the fabric surface, The subsequent dyeing of the surface with Rhodamine B causes a further increase of this interaction to gamma(s)(-) = 70.6 mJ/m(2). Rhodamine B contains two amine groups and one carboxyl group which can strongly interact with the polyester surface as well as with the adsorbed tannic acid molecules, Because of the cationic character of Rhodamine B molecules, the electrostatic interaction with the negatively charged polyester surface plays an essential role, The thin-layer method for determining the surface free energy components of the fabric appeared to be very useful, especially because the contact angle method cannot be applied here.