Carnosic acid (CA) along with carnosol (CAR) is the strongest phenolic diterpene antioxidants (PDAs) present in rosemary plant. However, CA has low antioxidant activity in emulsion-type food system due to its polar nature. The identification and characterization of the anticancer and antimicrobial properties of natural products and their semisynthetic derivative such as that of CA and CAR have received significant interest over the years. The goals of this research were to synthesize lipophilic palmityl derivative (PE) of CA and study its antioxidant activity in bulk and emulsified corn oil. Anticancer properties against CCRF-CEM, K-562 and P388D1 leukemia cell lines and antimicrobial activity against Staphylococcus auerus (S. auerus), Bacillus cereus (B. cereus), Salmonella enterica, and Escherichia coli (E. coli) O157:H7 bacteria were also tested. A four steps synthetic route was designed. In the first step CAR was converted into a benzyloxy protected benzyl ester of CA (yield 78%). Reduction of the benzyl ester to a primary alcohol (yield 63%) followed by esterification with palmitoyl chloride gave the palmityl ester derivative (yield 97%). Finally, double bond reduction followed by deprotection of benzyloxy group gave PE (yield 99%). Overall yield for the route was 47%. The modification of CA affected functionality. PE had improved antioxidant activity in emulsified corn oil compared to bulk corn oil than the CA. However, CA was more effective in bulk oil. Compounds with hydroxyl groups were found to have cytotoxicity against three cell lines CCRF-CEM, P388D1 and K-562. Among compounds tested, CAR was found to be the most potent anticancer agent against all three cell lines. The study also indicated structure dependent activities for the compounds that had hydroxy group at the C-20 position. CA and CAR had antimicrobial activity against S. auerus, B. cereus, Salmonella, and E. coli O157:H7. S. auerus, B. cereus were more sensitive to CA and CAR than Salmonella, and E. coli O157:H7. Other compounds, without hydroxyl groups, did not have antimicrobial activity. Study also indicated that antimicrobial activity varied depending on functional group present at C-20 position. Compound PE did improve antioxidant activity in emulsion but did not improve antimicrobial activity.