This study aimed to determine the transmission characteristics of H9N2 avian influenza viruses (AIVs) derived from the air. Eight H9N2 AIVs were isolated from chicken houses between 2009 and 2010. We analyzed the phylogenic and pathogenic traits of these isolates. What is more, transmission characteristics in guinea pigs of two airborne isolates were determined in experimental conditions. Phylogenetic analyses indicated that the homologies of HA and NA genes of eight isolates were 95.4-99.7% and 86.6-99.8% respectively. They were able to duplicate in lung tissues of guinea pigs without prior adaptation. Two airborne isolates could both transmit among guinea pigs by direct contact. No infection was detected in aerosol contact animals while H9N2 AIV aerosols were detected in the air of isolators. Aerosol infection dose experiment showed that aerosol median infective dose (ID(50)) of H9N2 AIV to guinea pigs was 3.58×10(6)copies, demonstrating that the aerosols could infect guinea pigs at certain concentrations in experimental condition. In conclusion, H9N2 AIV aerosols were infectious to mammals, suggesting that urgent attention will need to be paid to its transmission. Copyright © 2012 Elsevier B.V. All rights reserved.