Oxidized single-walled carbon nanotubes (o-SWNTs) were employed as the drug carriers to deliver the small molecules of Rhodamine123 (Rho123) into the K562 cells via physical adsorption. However, due to the fluorescence quenching of Rho123 on carbon nanotubes, the quantitative determination of Rho123 in cells is difficult. Based on the MEKC coupled with LIF detection, a quantitative approach was developed for the determination of Rho123 delivered into K562 cells by o-SWNTs. Where the adsorbed Rho123 on o-SWNTs could be desorbed by SDS in running buffer and be simultaneously separated with o-SWNTs due to the differences of their electrophoretic mobility by applying the electric potential at the both ends of capillary. Using this approach, the intracellular uptakes of Rho123 in multidrug-resistant and multidrug-sensitive leukemia cells were quantified, and the results showed that o-SWNTs could be used as the potential drug carriers to deliver small molecules into cells via the physical adsorption along with the circumventing of multidrug resistance of leukemia cells.