The oil obtained from Evening Primrose seeds is a source of ?-linolenic (GLA; 18:3n-6) acid and, therefore, it enjoys widespread use in pharmacy and in the production of cosmetics. Gamma-linolenic acid is an important unsaturated fatty acid with active ingredients. It is an essential acid for maintaining the normal physiological functions of the human body. Gamma-linolenic acid and its metabolite play an important and extensive physiological role in the immune system, the cardio-cerebral system and the endocrine system of the human body. Gamma-linolenic acid is an important intermediate in the human metabolic pathway that converts dietary linoleic acid (LA) into prostaglandins. The bioconversion of linoleic acid to Gammalinolenic acid is catalyzed by the enzyme delta-6-desaturase; but several factors, including aging, diabetes, alcoholism, atopic dermatitis, rheumatoid arthritis, cancer and cardiovascular disease can reduce or inhibit the activity of this enzyme, leading to a variety of ailments. Dietary supplementation of Gamma-linolenic acid with naturally derived oils has been reported to be of value in treating several pathological conditions. Gamma-linolenic acid is found in human milk and in small amounts in a wide variety of common foods, notably organ meats. It is found in relatively high abundance in the plant seed oils of evening primrose (7– 14g/100 g GLA), blackcurrant (15–20 g/100 g GLA), borage (18–26 g/100 g GLA) and fungal oil (23–26 g/100 g GLA). Although there are other sources of Gamma-linolenic acid, evening primrose oil appears to be the most biologically active. The process of oil production, especially conventional extraction methods, can cause several chemical reactions in the oil components, such as the degradation (autooxidation and photooxidation) of Gamma-linolenic acid. In this study, supercritical fluid extraction (SFE) with carbon dioxide has been employed to recover evening primrose seed oil (EPO). The effective variables of temperature (33-61 ?C), pressure (7.5-39.5 MPa), static time period (5-45 min) and dynamic time period (30- 150 min) were optimized by a factorial design method. Extraction were performed with CO2 flow rate of 1.5 ml/min and vessel was packed with 60 percent of crushed glass. A partial factorial design was used to design the experiment and a mathematical model was constructed to relate the extraction yield to the variables. The .