Abstract: 【Objective】The changes of the contents of the functional substances including lycopene, citrulline and ascorbic acid (VC) of watermelon during fruit development were studied in order to provide a theoretical basis for optimization of watermelon breeding. 【Method】The contents of lycopene, citrulline and ascorbic acid (VC) of watermelon during fruit development were analyzed. The lycopene, citrulline and total ascorbic acid (TAA) contents were determined by spectrophotometry methods and ascorbic acid (AA) was determined by 2,6 - dichlorophenolindophenol titration. 【Result】The lycopene accumulation during fruit development of red flesh watermelon fruit was a S-type curve. The lycopene content of young fruit was low, and slow accumulation during fruit development, then lycopene content increased dramatically with the red flesh coloring and achieved the highest value at ripening stage. Decreasing tendency in lycopene contents was observed during overripening. The citrulline contents of young fruits were lower, then it accumulated slowly during fruit development and decreased in fruit enlargement. Then it increased rapidity and achieved the peak value before maturity. The decreasing tendency in citrulline content was noticed in maturity phase. The change of VC contents in different color flesh of watermelons were showed a M-curve shape during fruit development: The content of total ascorbic acid (TAA) in young fruit was high, then reached the first peak of TAA content with the enlargement of the fruit, The TAA contents decreased rapidly to the lowest level and then increased rapidly to achieve the second peak at ripening stage. The decreasing tendency in content was noticed during overripening. Both ascorbic acid (AA) and dehydroascorbic acid (DHAA) contents showed the same change. When achieved the peak, the ratio of TAA﹕AA contents in different fruits of watermelon varieties were about 1-2﹕1. 【Conclusion】The contents of lycopene and V
C in ripe fruits of watermelon achieved the peak value and the contents of citrilline in nearly mature of watermelon fruit achieved the peak value.

Key words: Watermelon, Lycopene, Citruline, Vc