Abstract：PM2.5 samples were collected in forest and urban areas in Nanchang City in March April 2021 in thisstudy.The concentrations of FAAs （free amino acids） in PM2.5 were determined. The results showed that the concentrations of FAAs ranged from 0.093 nmol·m-3to 0.885 nmol·m-3 and 0.393~1.316 nmol·m-3 in the forest and urban area， respectively. The average concentration of FAAs in PM2.5 collected from the forest area （（0.451±0.197） nmol·m-3） was significantly lower than that in the urban areas （（0.586±0.227） nmol·m-3） were. The composition of amino acid in the forest and urban was similar. Pro was the most abundant amino acid， followed by Gly， Ala， Val， Leu and Ile. The percentage of hydrophobic amino acids in urban areas （46.25%）were much higher than that in forested areas （41.57%）， suggesting that hydrophobic aminoacids prefer to accumulated in urban aerosols. The positive correlation between temperature and FAAs in PM2.5 was found in the urban area （p<0.05）， indicating temperature had significant influence on FAA concentrations. Moreover， O3 positively correlated with FAAs in the urban （r=0.6， p<0.01）， indicating that FAAs might participate photochemical reaction process in the urban aerosols. According to the backward trajectory analysis， the concentrations of FAA in forest areas above 2000 m was significantly higher than that of below 2000 m （p<0.05）. In urban areas， FAA from above 2000 m and below 2000 m accounted for the same proportion of concentrations.