Abstract: Eeffect of octenyl succinic acid modified starch on quality of margarine as the fat substitute were studied,discussed the influence of replacement on foam overrun,fat globules partial coalescence,thixotropic behavior,texture characteristics and crystal characteristics of margarine. The result showed that,with the increase of octenyl succinic acid modified starch level,the sensory quality,foam overrun,fat globules partial coalescence and foam firmness of margarine were found to be decreased,while the thixotropy-loop area to be increased.All indexes were significantly altered over the 12% replacement. In this paper,based on comprehensive consideration of sensory quality,whipping properties,crystallization stability,the suitable range of thixotropy-loop area and foam firmness,the optimum fat substitute rate of octenyl succinic acid modified starch in margarine was 12%.