Salvianolic acid B (SalB) is an active component isolated from Chinese herbal medicine Salvia miltiorrhiza. The aim of this study was to investigate the extent of absolute oral bioavailability (F) of SalB in beagle dogs and the effect on blood viscosity after intravenous and oral administration of Salvianolic acids (SAs). A gradient elution HPLC method was developed and validated to determine the concentration of SalB and its three possible metabolites in plasma. After SAs (180 mg/kg, p.o.; 9 mg/kg, i.v.) were given, the AUCs of SalB were $1680;{pm};670$ and $7840;{pm};1140;ng/mL{cdot}h$, respectively. The F of SalB in dogs was calculated to be only $1.07;{pm};0.43%$. The blood viscosity was remarkably decreased after a single intravenous injection of SAs (9 mg/kg). However, no significant change of blood viscosity was observed after a single oral administration of SAs (180 mg/kg). The results suggested that the F of SalB was extremely low and single oral administrated SAs had no effect on ameliorating blood viscosity in beagle dogs.