Abstract: Background: Herbs have been used for several purposes i.e., flavorings, beverages, repellents, fragrances, cosmetics and for their medicinal properties. Now a days, the interest in herbs has considerably increased, particularly as a natural source of flavor and antioxidants for the food and pharmaceutical industries. The quality and acceptability of food are related to flavor stability. It is well known that, manufacturing and storage processes, package materials and ingredient of foods often reduce aroma compound intensity. In order to minimize aroma degradation or loss during processing and storage, it is beneficial to encapsulate volatile ingredients prior to use in foods or beverages. Objective: This study aimed to investigate the effect of using different carrier materials on chemical composition, thermal stability and antioxidant activity of nano-encapsulated rosemary essential oil. Methodology: About 100 g of rosemary was subjected to hydro-distillation using Clevenger apparatus for 4 h to isolate its essential oil. Essential oil sample was analysis by GC-FID and GC-MS. The nano-encapsulation was procedure by homogenization technique in all samples. Encapsulation Efficiency (EE), Transmission Electron Microscopy (TEM), DPPH scavenging activity and total phenolic content of encapsulated essential oil samples were evaluated. Thermal stability assessment was done by Differential Scanning Calorimetric (DSC). Results: The results revealed that the highest release of total phenol (3349.4 μg GAE mL–1) and DPPH scavenging activity of rosemary EO were found in case of using chitosan as carrier material for nano-encapsulation process compared to CMC or sodium alginate. Also, the nano-encapsulation process improved thermal stability of rosemary EO. The TEM of nano-encapsulated of rosemary EO in CMC showed the lowest nano-particle size (10-20 nm) compared with chitosan or sodium alginate. After the GC-MS analysis of the volatile compounds of rosemary EO revealed that 1,8-cineole (30.88%), camphor (22.71%), α-terpineol (15.01%), α-pinene (8.78%) and camphene (4.31%) were the major compounds in rosemary EO. The results showed an increasing content of oxygenated monoterpenes, sesquiterpenes, sesquiterpene oxide and ester in nano-encapsulated rosemary EO samples. An opposite behavior was observed in content of monoterpens. Conclusion: In this study, the major components of rosemary EO were 1,8-cineole (30.88%), camphor (22.71%), α-terpineol (15.01%), α-pinene (8.78%) and camphene (4.31%). The type of wall materials has influence on the particles size and encapsulation efficiency and antioxidant activity of rosemary EO. The results indicated that nano-capsulation process increased the thermal stability of rosemary EO and could be useful as antioxidant for various thermal processing applications in industry.