Abstract: The effects of enhanced UV-B radiation on basic chemical components, chromoplast pigment and phenols contents were studied in the leaves of two flue-cured tobacco cultivars — “Yunyan 87” (Y87) and “Honghuadajinyuan” (HD). Selected cultivars were exposed to UV-B radiation at ambient (control, CK), ambient plus 5.30 kJ?m^-?2?d^-?1 (T1) and ambient plus 8.50 kJ?m^-?2?d^-?1 (T2) levels that respectively simulated 24.65% and 39.53% ozone depletions under summer solstice field conditions in Kunming City (located at 25?04?N and 102?73?E). The study was meant to provide theoretical basis for the formation mechanism of chemical quality of flue-cured tobacco leaves in different ambient UV-B regions. Water soluble total sugar and catechol levels declined markedly in leaves of both cultivars with two doses of UV-B radiation compared with CK. However, total nitrogen, potassium, free amino acids, chromoplast pigment and flavonoid levels increased in leaves of both cultivars. While nicotine level increased in the leaves of Y87, it decreased in the leaves of HD under two doses of UV-B radiation compared with CK. Changes in water soluble total sugar and total nitrogen levels in response to UV-B radiation suggested that Y87 was more sensitive to UV-B stress than HD.