The aggregation patterns of sodium taurocholate (TC) and taurodeoxycholate (TDC) in an isotonic sodium chloride solution at 298.2 K are investigated by frontal derivative chromatography on Sephadex G-10 columns and are quantitatively analyzed on the basis of several aggregation models. The aggregation parameters are best fitted to the observed centroid volume data. The derivative chromatogram of TC at 6.006 mM simulated on the basis of a stepwise aggregation model is in excellent agreement with the observed one, whereas the simulation on the basis of the pentamerization model remarkably differs in shape from the observed one. The derivative chromatograms of TDC at 1.500 and 2.003 mM simulated on the basis of another stepwise aggregation model are closer to the observed ones than those of the Bottari-Festa model. Thus, TC and TDC form their dimers and polydisperse micelles. These conclusions are supported by the fitness to the centroid volume data. In light of the present results and current reports, the structure and counterion binding of bile salt micelles are discussed.