This study evaluated the oxidative stability of butter with added phenolics from Lamiaceae herbs. Initially antioxidant activity of crude rosemary, oregano, sage, thyme and marjoram extracts were screened through methods of inhibition of the 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical, malondialdehyde (MDA) quantification and ferric reducing antioxidant power test. The alcoholic extract of rosemary showed the highest antioxidant activity in both assays for DPPH radical inhibition and MDA quantification. The alcoholic rosemary extract showed no cytotoxicity when assayed using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] reduction method and had dose-dependent cytoprotective activity at 50 and 250 μg mL−1. These results suggest that the use of rosemary as natural antioxidant is safe in the concentrations tested. The highest oxidative stability of butter with added alcoholic rosemary extract at temperatures of 60 and 110 °C was obtained with the concentration of 400 mg of phenolic compounds per kg of butter and was reflected at the lowest formation of degraded peroxides from lipids.