Watermelon contains lycopene, a red carotenoid pigment that has strong antioxidant properties. The lycopene content of watermelon is substantial, contributing 8−20 mg per 180 g serving. There are no reports on carotenoid changes in whole watermelon during storage. Three types of watermelon, open-pollinated seeded, hybrid seeded, and seedless types, were stored at 5, 13, and 21 °C for 14 days and flesh color, composition, and carotenoid content were compared to those of fruit not stored. Watermelons stored at 21 °C had increased pH, chroma, and carotenoid content compared to fresh fruit. Compared to fresh fruit, watermelons stored at 21 °C gained 11−40% in lycopene and 50−139% in β-carotene, whereas fruit held at 13 °C changed little in carotenoid content. These results indicate that carotenoid biosynthesis in watermelons can be affected by temperature and storage.