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In order to select the best period for selenium（Se）application for winter jujube（Ziziphus jujuba Mill. var. Dongzao）, a field ex⁃ periment was conducted to study the effects of different Se application（via foliar spraying）periods on total Se content, organic Se ratio, and fruit quality. The NaSeO3 solution（27 mg Se per plant）was applied only once at different growth stages including leaf expansion period （LEP）, fruitlet period（FLP）, fruit swelling period（FSP）, and fruit ripening period（FRP）. The results indicated that total Se content in leaf and fruit increased rapidly when the Se foliar spray was applied at FSP or FRP, and the maximum values were observed when Se was applied at FSP. The Se content in fruit was enhanced from 25 μg·kg-1 to 76 μg·kg-1. Various effects on the fruit quality of winter jujube were found depending on different Se application periods. Foliar Se spray application at FSP showed the best effects for improvement of fruit quality yielding the maximum values of soluble solid, soluble sugar, vitamin C, total flavone content and sugar-acid ratio, which were significantly higher by 13.30%, 17.17%, 16.33%, 29.17%, and 28.89%, respectively, in comparison to that in the control. These results suggested that foliar NaSeO3 spray, at a Se concentration of 45 mg Se·L-1, applied at FSP was a good method for the production of Se-enriched winter jujube fruits. [ABSTRACT FROM AUTHOR]