Camptothecin (CPT) is a potent chemotherapeutic agent that shows a broad spectrum of anticancer activities. However, it is clinically inactive because of poor aqueous solubility, rapid aqueous hydrolysis, and unexpected side effects. Three strategies have extensively been adopted to improve its dissolution rate including reduction of drug particle size to a nanoscale, use of an amorphous state, and the formation of inclusion compounds. In our study, we combined these three strategies together by constructing CPT nanoparticles by creating an inclusion complex with β-cyclodextrin (BCD). This new CPT formulation showed a rod-like structure of nanoscaled size and with semiamorphous or amorphous CPT. These BCD–CPT nanoparticles showed improved dissolution rate, stability, dispersion, and cellular uptake. When tested on cancer cells, BCD–CPT nanoparticles showed a much higher anticancer activity (IC50=14–28 μmol/l) in comparison with free CPT (IC50>500 μmol/l) and CPT nanocrystals (IC50>200 μmol/l). In addition, BCD–CPT nanoparticles can be physically mixed with CPT nanocrystals, leading to CPT formulations with tailored drug-release profiles to achieve customized therapeutics and flexible treatments in clinics.