The physical stability of the chitosan modified nanocrystals was remarkably improved under ambient conditions. During the in vitro dissolution test, the modified nanocrystals showed a certain degree of slow-release property. In the in vivo study, the Cmax of nitrendipine remained the same, however, the Tmax delayed from 0.75 h to 1.5 h with the chitosan modified nanocrystals. The surface modification by chitosan improved the bioavailability compared with the initial nanocrystals, which had demonstrated significant improvement of bioavailability compared to the traditional coarse powder form. Based on the experimental results, modification of the nanocrystals with certain polymer was supposed to be a good method to control the in vitro and in vivo behaviors of the nanocrystals, which could further increase the bioavailability of the water insoluble drug.