Two domestic dogs in China were identified with evidence of H1N1/2009 influenza virus infection in November 2009. Virus isolation and sequence analysis of all eight genes of the two isolates showed that they were closely related to those of H1N1/2009 influenza virus circulating in humans, and therefore that they were likely acquired from humans. To determine the pathogenicity and transmissibility of H1N1/2009 influenza virus in dogs, experimental infection and transmission was performed. Inoculated dogs were able to shed virus in nasal secretions, but symptoms were very mild. Uninoculated dogs were comingled to determine the transmissibility of the isolate and one of three exposed dogs was shown to develop infection. The present findings indicated that human H1N1/2009 could infect dogs, but transmitted inefficiently between dogs