Epidemiological investigations show that long chain (LC) ? 3 PUFAs have beneficial effects on health and prevention and therapy of many diseases, especially cardiovascular types. Due to high oxidization susceptibility and undesirable aroma of these fatty acids, enrichment of foods with those sources, has an unattractive effect on sensory properties of enriched foods. It has been shown that microencapsulation, protect them against oxidation. In this study, LC ? 3 PUFAs was microencapsulated using complex coacervation technic. A four components (acacia gum, gelatin, fish oil and water) mixture design was used to determine optimum mixture components to achieve maximum value of microencapsulation efficiency (ME), oil content (OC) and payload of microcapsules. Initial experimental design was chosen in order to cover a large range of mixtures. At first, fish oil was emulsified in a 10% gelatin aqueous solution (50°C); then acacia gum solution (50°C) was added to it, and mixture pH decreased to 4. Mixture temperature and mixer rotation speed were then adjusted on 50°C and 600 rpm, respectively for 15 minutes. Microencapsulation was finished by cooling down the mixture to 4-7°C and then stirring was stopped. Obtained suspension or gel was lyophilized and grinded. Surface oil of microcapsule powder was extracted using n-hexane in order to measure ME. Encapsulated fish oil was added to milk to provide 0.2 gram EPA plus DHA/day based on EANS recommendation for 12 serving yogurts per week. Physical properties, peroxide value, sensory acceptance and release of fish oil from added microcapsules to yogurt were measured in enriched yogurt during 21 days storage. ME, OC and payload were found in ranges of 16-92%, 15-50% and 18-104% respectively. A special cubic model was found to describe the effect of components on founded results. By increasing encapsulants and reducing fish oil and water in formulation, ME increased and then after, it decreased. Increasing gelatin content in formulations comparing acacia gum had more effect on optimum ME. Relative optimum points for gelatin to acacia ratio and encapsulants to fish oil ratio were in ranges 1.49-3.04 and 0.49-1.67, respectively and it isn’t necessary to increase encapsulants concentration to higher than 6.8%. At constant concentration of encapsulants, increasing fish oil in formulation, cause an increase in microcapsules size. Acidity, apparent viscosity and WHC of enriched samples were higher and gel strength and amount of syneresis were lower than control. The enriched yoghurt samples were more yellowish comparing to control. The peroxide value of enriched yogurt samples with free and encapsulated fish oil after 22 days storage at 4°C were increased to 72% and 260%, respectively. No fish oil was detected in extracted oil from yogurt samples. Sensory results shows that panelists evaluated enriched yogurt with lime juice-treated fish oil microcapsules as ‘low to moderately liked’.