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• Foliar spraying of sodium selenite significantly increased the apple quality. • Foliar spraying of sodium selenite effected the physicochemical indicators, and finally determined the apple quality. • Sucrose metabolism significantly correlated to the activities of key enzymes, SPS is a crucial enzyme. • Sodium selenite dose ranged from 100 and 150 mg/L could be appropriate. Selenium is an essential trace element that improves fruit quality and nutritional value. However, the effect of sodium selenite on apple quality and its relative sucrose metabolism activity remains unclear. In this study, we investigated the roles of selenite spraying, in improving Fuji apple quality and sucrose metabolism-related enzyme activity. Results showed that foliar spraying of sodium selenite significantly (P < 0.05) increased apple fruit yield and internal quality, but no significant effects on external quality. The apple yield, vitamin C content, sugar-acid ratio and total soluble sugar increased 4.4% to 11.7%, 4.68% to 20.86%, 3.07% to 31.57%, and 4.53% to 18.89%, respectively. Se content is 9.5-fold compared to the control. Significant correlations were observed between neutral invertase, sucrose synthase activity and sucrose phosphate synthase enzymes, and sucrose phosphate synthase enzyme was most crucial. Spraying sodium selenite of 100–150 mg/L could be appropriate for improving Fuji apple yield and quality. [ABSTRACT FROM AUTHOR]