Abstract: In this study,the potential use of an aqueous two phase system( ATPS) coupled with ultrasound for the extraction of β- carotene from Spirulina platensis was evaluated and optimized using response surface methodology( RSM). Box- Behnken Design was applied to evaluate the effects of four independent variables( ethanol concentration( %,w/w),n- butanol concentration( %,w/w),ratio of material to solution( g /m L),ultrasonic time( min) on β- carotene extraction yield.The optimal conditions were 8.2%,36%,1∶20( g / m L) and 3 min for ethanol concentration,n- butanol concentration,ratio of material to solution and ultrasonic time respectively.β- carotene yield was determined to be 3.13 mg / g under the optimal conditions.The results indicated that Spirulina platensis β- carotene would be purified by a simple,efficient extraction technology using inexpensive ethanol /n- butanol ATPS.