Abstract：The unique bitterness of lettuce（Lactuca sativa L.）comes from sesquiterpene lactone compounds，mainly including lactucopicrin and lactucin．In order to investigate the regulating effect of ultraviolet light on growth of lettuce and sesquiterpenoids，this paper took pure red light（180 μmol · m-2 · s-1）as the contrast；compared the effects of supplying UV-A（30 μmol · m-2 · s-1）or UV-B（10 μmol · m-2 · s-1） on the growth and sesquiterpenoids content of 7 lettuce species；and further analyzed the compensation light intensity of UV-A to infrared light（15，30，45 μmol · m-2 · s-1）and supplementary light duration（0，1，2，3，6，9 days）on the content of sesquiterpenoids in lettuce．The results showed that UV-A supplementation could significantly increase the fresh quality of‘Lvluo’above ground，significantly reduce lactucopicrin and lactucin contents of 7 lettuce varieties，by 33%-74% and 29%-60%，respectively．Along with the increase of UV-A supplementary light intensity，the content of sesquiterpenoids in lettuce decreased gradually．After the treatment of adding 30 μmol · m-2 · s-1 UV-A for 2 days，the lactucopicrin in lettuce increased rapidly．The peak value was reached after 3 days of treatment，then gradually decreased．While，the content of lactupicrin basically maintained a gradually increasing trend after 2 days of treatment．It decreased slightly after 6-9 days of treatment．In conclusion，supplying appropriate amount of UV-A（30 μmol · m-2 · s-1，3-6 days）to red light can significantly reduce the content of sesquiterpenoids in lettuce without affecting its biomass，thereby to lessen the bitterness．
