The effects of the harvest time and storage temperature on the elasticity index (EI) and fruit quality were investigated to develop a quality retention technique for ‘Aikou’ mango. All fruits used in this study were individually wrapped in polyethylene film (11 μm thick). Fruits harvested at the pre-natural fruit drop stage (FH-pre-NFDS) and the post-natural fruit drop stage (FH-post-NFDS) were kept at 25°C for 10 days. In ‘Irwin’, the EI at both harvest times declined to around 80 × 10⁵ and 72–75 × 10⁵ after 2 and 10 days of storage respectively, whereas in ‘Aikou’, the rate of decrease was greater than that of ‘Irwin’, declining to 43–46 × 10⁵ after 10 days of storage at both harvest times. In ‘Aikou’, the EI declined as the fruit ripening progressed and it was not influenced by the fruit size. When fruits were kept at 20°C for 0–10 days, the EI declined as the storage period extended, and it declined to 51–52 × 10⁵ at 10 days of storage. Flesh firmness also declined as the storage period extended, and its change was synchronized with the EI. When the FH-pre-NFDS were kept at 15–25°C for 10 days, the EI declined rapidly; however, the rate of decrease in the ones kept at 10°C was slower than the others, and the EI was significantly higher after 4 days of storage. The FH-Post-NFDS kept at 10°C showed the second highest EI. The a-value of the FH-pre-NFDS kept at 10°C remained low, and was lower than that of the others. Hot water treatment (55°C) for 10 or 15 min did not affect the EI or fruit quality. A highly positive correlation was found between the EI and flesh firmness. The results of this study show that maintaining at 10°C after 15–20°C for a few days for coloring may be effective for the inhibition of softening in ‘Aikou’ FH-pre-NFDS, and the EI is useful to evaluate the firmness of juicy and soft fleshy mango fruit.