Grapefruit is one of the vital citrus fruit which cultivated in many countries including Pakistan. Conversely, the shelf life of this fruit is rather short under ambient condition. The objective of this study was to extend the fresh fruit quality of grapefruit by using a natural wax coating substance like chitosan. The coating of chitosan in extending the postharvest life of grapefruit was investigated in relation with the phytochemicals like total phenolic compounds (TPC), total antioxidants (TA), total carotenoids (TC), total flavonoids (TF), etc., and physiological changes including chilling injury (Cl), weight loss (WL), and gases exchanges. The experiment was intended in a completely randomized design, composed of coating with chitosan at three levels, and stored at 8°C with relative humidity is 95.5%. The results indicated that chitosan application @ 140 mg per fruit maintained the highest fruit quality parameters such as, TPC (172.32 mg GAE/100g), TA (72.09%), TC (17.09 mg/100g), TF contents (52.27 mg CEQ/100g), total limonin contents (15.08 µg/mL) with minimum chilling injuries (1.58 %), and fruit rots (0.66%) were also measured. Overall, fruits coated with chitosan had greater external adequacy than untreated ones. The application of the chitosan @ 140 mg per fruit could be used to reduce deteriorative processes, maintain quality and increase the storage life of grapefruit at 8°C.