Abstract: The changes of free amino acids in burley tobacco with or without casing during roasting was studied by reverse phase high performance liquid chromatography with precolumn derivatization with o-phthalaldehyde and fluorenylmethyl chloroformate.The results showed that:1) the total amount of free amino acids in burley tobacco without casing increased first and then decreased in the process of roasting,and it decreased by 19% after tobacco was roasted for 18 minutes,and the contents of Asn,Asp and Arg decreased by more than 20%;2) for burley tobacco with casing,the total amount of free amino acids reduced gradually during roasting,and it decreased by 37% after tobacco was roasted for 18 minutes,and the contents of Glu and Phe decreased by more than 50%,Asn and Val decreased more than 40%,and Asp,Ser,Arg,Lys and Pro decreased more than 30%;3) the change of free amino acids in burley tobacco with or without casing mainly occurred at 140℃.