The effects of flesh color, season, and test cross on carotenoid, sugar, and ascorbic acid contents of 20 watermelon genotypes with red, pink, orange, and yellow flesh were examined. Red- and pink-fleshed watermelons contained lycopene (4.8-47.8 ${mu}g{cdot}g^{-1}$ fresh weight), ${eta}$-carotene (< 3.7 ${mu}g{cdot}g^{-1}$), and lutein (< 0.9 ${mu}g{cdot}g^{-1}$) as the major carotenoids. The orange and yellow watermelons contained complex mixtures of prolycopene, lycopene, and ${eta}$-carotene with levels less than 7.4, 1.5, and 8.5 ${mu}g{cdot}g^{-1}$, respectively. There were also minor carotenoids, such as violaxanthin, lutein, neurosporene, and zeacarotene in the range of 0-1.4 ${mu}g{cdot}g^{-1}$. Total sugar contents ranged from 24 to 91 ${mu}g{cdot}g^{-1}$, with sucrose, glucose, and fructose as the major sugars. The sugar profiles were divided into sucrose-, fructose-, and non-dominant groups. Higher percentages of glucose and fructose were negatively correlated with the total sugar content. Fairly-low levels of ascorbic acid, less than 28.2 ${mu}g{cdot}g^{-1}$, were measured, and some genotypes had nearly no ascorbic acid. There were only slight differences in ascorbic acid, sugar, soluble-solid, and total-carotenoid contents among 11 genotypes harvested in June and November. Five sets of test crosses showed various trends of heritability of carotenoids, sugars, and ascorbic acid in $F_1$ hybrids. In general, carotenoids and total sugar content tended to be inherited from the parent with lower carotenoid and sugar contents, respectively. Paralleled chemical analyses will be beneficial for efficient progress in breeding efforts and genetic research.