The antimicrobial and antioxidant effect of Majorana syriaca extract, obtained by ethyl acetate, to Yellowfin tuna was examined. The extract was added to refined corn oil at different concentrations (0–3900 ppm). Minced tuna was mixed with corn oil containing the extract (tuna/oil: 3/1 w/w); the mixture was packed aerobically and stored at 0 °C. Microbial growth and lipid oxidation were determined periodically. Majorana syriaca extract delayed the microbial growth (total viable count, Pseudomonas sp. and lactic acid bacteria) as compared with pure minced tuna, with an increasing effect as concentration increased. Oxidation was monitored through measurement of peroxide value and thiobarbituric acid-reactive substances. Both tests showed inhibition of tuna oxidation as the concentration of the extract increased. The results of the study show the potential of M. syriaca extract in extending the shelf life of tuna fish.