Abstract: To investigate the appearance characteristics of fully mature flue-cured tobacco leaves growing in Guangdong, the effects of harvesting time on the enzymes key to carbon and nitrogen metabolism and main chemical components in flue-cured tobacco were studied with field experiments. The results showed that:except for middle leaves, the amylase activity in tobacco leaves increased gradually, while nitrate reductase (NR) activity in tobacco leaves raised first, then declined with the delay of harvesting time. The delay of harvesting time was beneficial to reducing starch and total nitrogen contents, increasing total sugar and reducing sugar contents, and promoting nicotine accumulation. In upper leaves, amylase activity significantly negatively correlated to starch content, while NR activity extremely significantly positively correlated to total nitrogen content. In middle leaves, NR activity extremely significantly negatively correlated to starch content, while extremely significantly positively correlated to nicotine content. In lugs, amylase activity extremely significantly positively correlated to total sugar and nicotine contents, while extremely significantly negatively correlated to total nitrogen and protein contents. The current standard of leaf harvesting was proper for flyings, however, it was recommended to delay for 5-10 days for lugs, middle and upper leaves. Meanwhile, the appearance characteristics of mature flue-cured tobacco leaf in Guangdong were proposed.