Abstract: To explore the relation between the accumulation of lycopene and hormones，genotypes with different ploidy（2x，3x，4x）watermelon‘Mimei’were used as materials. The content of endogenous hormones（IAA，ABA，GA，ZR，BR）and lycopene were tested by ELISA（enzyme linked immunsorbent assay）and spectrophotometry respectively during the fruit development period. The results showed as follows：The fruit reached its full size from 25 d to 30 d after pollination. The content of lycopene had the tendency of triploid（3x）> tetraploid（4x）> diploid（2x）and rapidly increased at 25 d after pollination. The content of IAA in diploid watermelon was less than others during fruit developing period，and the contents of triploid were significant more than others at 15 d and 25 d after pollination；There was no obvious regularity about the content of ABA among different ploidy；The content of GA reached the maximum in the early development period，but decreased gradually as the fruit grows；The content of ZR had no obvious difference among different ploidy in the whole development，only having a peak value at 25 d after pollination；The content of BR was less than other hormones in watermelon fruit，maintaining in 5–15 ng ? g-1FW during fruit development period. There was a negative correlation between lycopene and GA. The correlations between lycopene and others hormones were not found.

Key words: watermelon, ploidy, lycopene, endogenous hormone, correlation