An in-liquid curing method was devised to prepare a CM-chitin microsphere for sustained-release of anticancer agent. 6-Mercaptopurine (6-MP) as a reference core was incorporated into the gel by the ionotropic crosslinking with ferric chloride. Drug release rate of the CM-chitin microspheres decrease with increasing concentration of iron(III)-chloride solution and the curing time. Iron elution from the complex CM-chitin beads decrease from pH 1.2 to pH 7.5, especially between pH 4 and pH 3, because the iron(III)-CM-chitin complexes are unstable in acid medium. The drug-release patterns of the CM-chitin microspheres in pH 7.2 seem not only to be diffusion influenced but also macromolecular relaxation influenced. Whereas, release profiles of the microspheres in pH 1.2 medium seem to be matrix erosion controlled but are also affected by crosslinking density of the microspheres. The effect of lysozyme degradation is not obvious. These results indicate that CM-chitin might prove useful as a polymer carrier for the sustained release of anticancer drugs in various dissolution medium.