Ozone is a powerful oxidising agent, which can kill microorganisms if they are exposed to a high enough dosage for a sufficient period of time. So, this study was carried out during 2020-2021 seasons to explore the effect of different doses of gaseous ozone (10, 20, and 40 ppm for 15, 30, and 45 min, respectively) on physicochemical properties, maintaining quality and prolonging storage period of fresh cut “Hass" avocados during cold storage conditions at 5 ± 1°C with 85-90% RH for 28 days. Fruit quality attributes of slices “Hass" avocados measured were soluble solids content percentage (SSC %), total acidity percentage (TA %), ascorbic acid content (vitamin C, mg/100gFW), chlorophyll a, b and total carotenoids content (TCC, mg/g FW), total phenolic content (TPC, mg /100gFW), and polyphenoloxidase activity (PPO, Ug/FW). In comparison to the non-ozonized avocado slices (control), ozone treatments showed a positive effect on extending the storage time of avocado slices with good quality attributes. At the end of storage period, the fruit slices exposed to ozone at 40 ppm for 45 min showed increased SSC %, PPO and ascorbic acid content, as well as reduced total acidity % and TPC. However, avocado slices exposed to 20 ppm ozone for 30 min had greater chlorophylls a, b, and total carotenoids. Ozone application could be an effective strategy for keeping up postharvest quality of fresh cut “Hass" avocados and extend the storage life. Therefore, it can be recommended to expose fresh avocado slices to ozone at 40 ppm for 45 minutes in order to maintain their quality for 28 days under cold storage conditions at 5 ± 1°C and 85-90% relative humidity.