Abstract: AIM　To prepare naftopidil bioadhesive sustained-release capsule and study their pharmacokinetics and relative bioavailability in the dog. METHODS　Bioadhesive polymers such as hydroxypropyl methylcellulse (HPMC) and Carbopol 934 (CP 934) were used in capsule prescriptions. Naftopidil capsule and two formulations of bioadhesive sustained-release capsules (I and II) were given to five healthy male dogs in a cross-over test. The naftopidil concentrations in plasma were determined by a newly developed HPLC method and the pharmacokinetic parameters as well as the relative bioavailability were measured. RESULTS　The C_0→∞, C_max and T_max of naftopidil capsule was (3728±573) h·ng·mL^-1, (697±94) ng*mL^-1 and (1.2±0.5) h. These parameters of bioadhesive sustained-release capsule I and II, respectively, were (5518±391) h·ng·mL^-1 and (5636±427) h·ng·mL^-1; (468±61) ng·mL^-1 and (512±72) ng·mL^-1; both (4.0±0.7) h. Results from statistics showed that there were significant difference between bioadhesive formulations and the non-bioadhesive one in C_0→∞, C_max and T_max. The bioadhesive formulations and the non-bioadhesive one were not bioequivalent, the relative bioavailability of the two bioadhesive sustained-release capsules were respectively 150%±14% and 154%±23% when compared with the non-bioadhesive capsule. CONCLUSION　It is much improving bioavailability of naftopidil by using bioadhesion.