Objective To investigate the pharmacokinetic parameters of oseltamivir and the efficacy of oseltamivir against influenza virus in tree shrews. Methods Tree shrews were orally administered oseltamivir for pharmacokinetic analysis, and then their pharmacokinetic parameters were compared with those of humans, ferrets, mice, and rats reported in the literature. The tree shrews were inoculated with human influenza virus A/ California/04/2009 H1N1 or avian influenza virus H9N2 Y280-PB2-E627K intranasally. Oseltamivir was orally administered twice a day for 5 consecutive days. Nasal symptoms of the tree shrews were observed, and the viral titer of nasal lavage was determined on 1, 3, and 5days after inoculation, the cell sedimentation of nasal lavage fluid was classified and counted. After 21 days of infection, the tree shrews were executed humanely and the serum antibody titers were determined by hemagglutination inhibition test.Results The pharmacokinetics of oral oseltamivir in tree shrews was as follows: C_max 1. 34 μg/ mL, T_max 0. 75 h, T_{1/ 2}2. 03h, and AUC_0-12 1. 76 mg·h/ liter. The viral shedding of tree shrews infected with H9N2 Y280-PB2-E627K virus was clearly inhibited after 1 day in the high-dosage oseltamivir treatment group, however, there was no clear inhibitory effect for A/California/04/2009 H1N1 virus. High-dosage oseltamivir treatment also reduced the nasal lavage fluid cell count of tree shrews infected with H9N2 Y280-PB2-E627K virus. The antibody titer of tree shrews infected with A/ California/04/2009 H1N1 virus was significantly higher than that of H9N2 Y280-PB2-E627K avian influenza virus. Conclusions The pharmacokinetic parameters of oseltamivir in tree shrews differ from those in humans and other model animals, such as ferrets, however, the T_max and T_{1/ 2}of oseltamivir in tree shrews were similar to those of mice. Oseltamivir can effectively inhibit the shedding of H9N2 Y280-PB2-E627K viruses and alleviate the inflammatory reaction in tree shrew nasal cavity.