Abstract: This paper dealt with the relation of the molecular structure of rosinate with the properties of sizing. The impact of the molecular structure and the ratio of functional group of rosinate on the sizing mechanism was inrestigated. The ratio of rosin and rosinate is the important effect factor to the properties of sizing in the rosinate neutral sizes. The best weight ratio is 40%~50%. The effect of sizing is best when the weight of malairosin is 7% through researching the effect of the weight of malairosin on the properties of rosinate neutral size emulsion.