In this study, stable 5-fluorouracil (5-FU)-loaded chitosan (CS)/alginate (Alg) nanoparticles (NPs) were prepared with poloxamer as a surfactant. The effects of the Alg concentration, CS/Alg weight ratio, and poloxamer concentration on the properties of the 5-FU-loaded CS/Alg NPs were studied. The results of dynamic light scattering and transmission electron microscopy indicated that stable 5-FU-loaded CS/Alg NPs of around 200 nm with low-size polydispersities were achieved. Furthermore, the in vitro release of the 5-FU-loaded CS/Alg NPs was investigated in phosphate buffer solution at pH 7.4. The results show that the encapsulation efficiency of 5-FU depended on the drug feeding amount (DFA), poloxamer concentration, Alg concentration, and CS concentration. However, the in vitro release rate of the 5-FU-loaded CS/Alg NPs was only related to the DFA, Alg concentration, and CS concentration and was independent of the poloxamer concentration. The time of 5-FU release from the CS/Alg NPs could be-controlled to be sustained for more than 12 h. According to this study, CS/Alg NPs stabilized by poloxamer could serve as a suitable candidate for the controlled release of 5FU. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2354-2359, 2010