The amino acid content and constitution of domestic flue-cured tobacco before and after the aging were investigated. The major amino acids of domestic flue -cured tobacco were histidine, serine, aspartic acid and proline and leucine, isoleucine and glycine were minority in them. Phenylalanine was the most changeable components through the aging. While the contents of tryptophan, sering and Proline which have herbaceous, harsh and bitter taste and aroma in smoke were reduced, tyrosine which adds smoothing and enhances smoke aroma was increased after the aging. The leaf tobacco aged at 4$0^{circ}C$ for 30 days had a amino acid composition as good leaf tobacco storaged in natural condition for 2 years.