Abstract: It is crucial to investigate the changes of contents and ratio of basic and acidic amino acids in aging process, and the ratio can be used to assess the quality of aged tobacco strips. Aiming to analyze these changes and their relationship with sensory quality, a study was conducted by using liquid chromatography to examine the variations in free basic and acidic amino acids of flue-cured tobacco strips in 2006―2008 from 12 regions, i.e. Longyan and Nanping (Fujian Province), Bijie (Guizhou Province), Sanmenxia (Henan Province), Yongzhou (Hunan Province), Liangshan (Sichuan Province), Ankang (Shaanxi Province), Baoshan and Qujing(Yunnan Province), Shandong, Chongqing, and Zimbabwe. Sensory evaluation results showed that aging time required for the peak sensory quality differed among the same tobacco grades produced in different years from the same region. In aging process, the ratio of basic amino acid content to acidic amino acid content gradually decreased, demonstrating a strong linear correlation with aging time and a significant correlation with sensory quality. Linear regression equations were adopted to calculate the range of basic and acidic amino acid ratios suitable for high-quality aged tobacco leaves in 2007 and 2008. After validating the samples in 2006, the judgment accuracy reached 85%. The ratio of basic to acidic amino acids can definitely measure the aging degree of tobacco leaves, which might provide a novel method for evaluating aging quality.