The azalide azithromycin was proved to be clinically effective against Gram-positive and Gram-negative bacteria. But the low bioavailability caused by its poor solubility and gastrointestinal response limited its application in clinic. With the purpose of increasing its saturation solubility and dissolution velocity, azithromycin was produced as nanosuspensions by high pressure homogenization. Nanosuspensions could increase the drug-loading and reduce the administration dosage, thus the gastrointestinal response could be minimized. In order to enhance the stability of the nanosuspensions, we got the freeze-dried powder by lyophilization. After dispersed in distilled water, the nanoparticles had a bulk population of about 400 nm and a spherical figure (watched by transmission electron microscopy). The analysis of differential scanning calorimetry and powder X-ray diffraction demonstrated that the crystal state of azithromycin had changed. In vitro release studies showed that the dissolution rate of nanosuspension, compared with micronized powder, had been obviously increased.