The purpose of this study was to prepare and characterize nanosuspensions loading the active lactone form of 10-hydroxycamptothecin (10-HCPT). Nanosuspensions were prepared in terms of microprecipitation-high-pressure homogenization method. As for the preparation processes, three important parameters, i.e. the agitation rate of stabilizer solution, homogenization pressure and cycle numbers, were investigated and optimized, and the optimal values were 1000 rpm, 1000 bar and 20 times, respectively. The particle size and zeta potential of the 10-HCPT-nanosuspensions were 131 nm and -25.5 mV. The particle morphology was determined by transmission electron microscopy and the 10-HCPT nanoparticles were baculine or trabecular in shape. The solid state of 10-HCPT in nanoparticles was analyzed using X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). The XRD and the DSC results both indicated that 10-HCPT was present as an amorphous state in the lyophilized powders for nanosuspension. The chemical stability tests demonstrated that near 90% lactone form of 10-HCPT was present in the nanosuspensions but it was easily transferred to the carboxylate form in the solution at pH 7.0-8.0. In vitro dissolution tests showed the dissolution rate of nanosuspensions, compared with the coarse suspensions, had been significantly increased.