CoQ10 is a lipophylic natural antioxidant with fundamental role in mitochondria bioenergetics. The positive effect of CoQ10 in therapy of some disease is due to its antioxidant and bioenergetics properties. By the ageing the endogenous synthesis of CoQ10 reduces and also foods cannot deliver enough CoQ10 for body. Therefore, food fortification is a natural way to compensate lack of CoQ10. Water insolubility, high melting point and yellow color are the main problems related to enrichment of food product with CoQ10. The objective of this study was to microencapsulate CoQ10 by complex coacervation method, using ?-lactoglobulin (?-lg) and Arabic Gum (AG). A four components (B-lg, AG, Oil containing Q10 and water) mixture design (Design Expert Ver(8.0.7) was used to determine optimum mixture component to achieve maximum value of microencapsulation efficiency (ME). At first CoQ10 powder was dissolved in (olive oil in order to prepare a 5 % solution. Then, it was placed opaque tube and stirred at 200 rpm at 37 ?C for 24h. Solutions of ?-lg and GA were prepared at 1-4% (W/V), by dispersing the required amount of ?-lg and GA in deionized water. The mixtures were stirred for 2 h at room temperature and rested over night at 4°C. The oil in water (o/w) emulsion was prepared by adding oil phase that containing CoQ10 to ?-lg solution and homogenizated at 14000 rpm for 2 min using an Ultraturrax T-18. Then GA solution was poured in to the O/W emulsion and stirred for 15 min at 300rpm. The pH of the mixture was adjusted close to 4 using 0.1 N HCl and the microcapsules were collected and freeze dried using freeze dryer at -45 °C for 24 h. Morphology of CoQ10 microcapsules was examined using Scanning Electron Microscope (SEM). An optical microscope was used to obtain images from moist microcapsules. Oil was extracted from microcapsules using n-hexane. About 0.2 g of extracted oil was dissolved in 1,4-dioxane and analyzed by High performance liquid chromatography (HPLC) system equipped with an ODS C18 column and UV detector. Microencapsulation efficiency (ME) was calculated for microcapsules based on extracted oil by n-hexane before and after freeze drying. The special cubic model was found to be the best model on the obtained results. It was observed that increasing encapsulating shell and reducing oil and water in samples, increased ME. Constant levels of oil were taken in consideration to determine ME changes at different zones. Oil content of microcapsules had an important effect on ME. Microcapsules containing lower oil contents (5-10%) increasing encapsulant (in tested range) resulted in decreasing ME and the best efficiency was achieved at low encapsulant concentrations and higher ?-lg:AG ratio. At higher oil (15-25%) contents in microcapsules, efficiency was increased by increasing each encapsulatly compound concentration to their maximum (4%) and at ?-lg:AG ratio of 1:1. Effect of oven drying and thawing on ME was compared to those found for freeze-dried microcapsules. Microcapsule with the highest ME was added to yogurt to assess the efficiency of complex coacervation method to produce microencapsules of CoQ10. In addition, release of CoQ10 to yogurt was measured during storage time. Added microcapsules could influences physical and sensory properties of yogurt, therefore these properties were studied during storage time. Acidity, apparent viscosity and hardness of enriched yogurts were higher than those of control samples. The enriched yogurt samples seemed more yellowish than the control samples. Measurement of released CoQ10 from microcapsules to yogurt indicates that 16.2% and 16.8% of total added CoQ10 were released to yogurt at 1st and 21st, respectively. Panelists graded the overall acceptance of the enriched yogurt as "average to desirable". Keywords : Complex coacervation, CoQ10, Microeancapsulation, Mixture design, Physical properties, Sensory evaluation , Yogurt