Changes in composition and sensory quality of buttercup squash(Cucurbita maximaDuch. ‘Delica') during fruit development and postharvest temperature and humidity conditions simulating shipment to Japan were studied at three representative growing sites in New Zealand. Fruit of a known setting date were harvested at 10‐day intervals and data were collected on heat accumulation, days after flowering, flesh colour, seed development, soluble solids, dry matter (DM) content, skin hardness, glucose, fructose, sucrose and starch content, and sensory properties before and after simulated shipment. Physical properties at harvest were related to sensory quality at the point of sale to identify an optimal harvest time. As fruit was left for longer on the vine the skin hardened, the flesh became redder, DM increased then decreased, the soluble solids and sucrose content increased and the sensory properties improved. Once harvested the flesh continued to become redder, sucrose and soluble solids increased, and starch and DM levels decreased. Starch and DM did not accumulate significantly after 40 days from flowering at any sites. Temperature accumulation affected the rate of increase in the maturity indicators measured. Sucrose levels, °Brix, and flesh colour varied too much with site and season to be used to indicate optimum harvest dates. Skin hardness and heat accumulation levels were the most effective means of estimating the optimum harvest date. The earliest time to harvest fruit to ensure an acceptable level of sensory quality after the simulated refrigerated shipment conditions imposed was at a skin hardness penetrometer score of 7 kgf. This point occurred between 240 and 300 growing degree days (base temperature 8°C) from flowering. Fruit harvested at this early stage required a postharvest ripening period to enhance sweetness and texture and to optimise sensory quality.