An interfacial free radical polymerization method was developed to fabricate polysaccharide nanocapsules, in which poor water-soluble drug of felodipine could be effectively encapsulated with good stability during storage. Exemplified by the preparation of felodipine-loaded N-maleoylchitosan (NMCS) nanocapsules, a felodipine/chloroform Mixture was dispersed in NMCS aqueous solution with the aid of a nonionic surface active agent. After charging initiator, the vinylated groups of NMCS were polymerized on the oil-water interface. As a result, felodipine was loaded into NMCS nanocapsule. The morphology and the size distribution of synthesized nanocapsules were characterized by field emission scanning electron microscopy (FESEM) and dynamic light scattering (DLS) techniques. The quantitative drug loading and sustained release behavior were investigated. The encapsulation efficiency and drug loading content were found to be strongly dependent on the feed felodipine concentration. The release dynamics showed strong correlation with the degree of maleoyl substitution and the feed NMCS concentration during the course of nanocapsules preparation.