Abstract Postharvest heat treatments by using hot water were applied to Thai lime fruit (Citrus aurantifolia Swingle cv. Paan) to investigate their effect on chlorophyll (Chl)-degradation and postharvest quality during storage. Mature green lime fruit were treated with water at ambient temperature (control) or with hot water at 50 °C for 3 and 5 min and then kept at 25 °C in darkness. The results showed that hot water treatment at 50 °C for 5 min efficiently delayed the decrease of hue angle values and the contents of Chl a. Activities of Chl-degrading enzymes including chlorophyllase, Chl-degrading peroxidase and pheophytinase as well as Mg-dechelation activity in lime fruit were reduced by hot water treatments. This reduction was more pronounced in fruit treated by hot water for 5 min than in those treated for 3 min. Moreover, heat treatments prolonged storage life by 5 days in fruit treated for 3 min and by 10 days in fruit treated for 5 min. Hot water treatment at 50 °C for 5 min maintained the highest total acidity and delayed the increase of total soluble solids contents during storage. Respiration rate and ethylene production were also reduced by the heat treatments. In conclusion, these results suggest that hot water treatment at 50 °C for 5 min could be a useful method to delay Chl degradation and to maintain postharvest quality in mature green lime during storage at 25 °C.