Abstract: The study of preparation of maleated rosins and their application as paper size was started in China in 1974. Distinguishing features in the preparation of maleated rosins in China, their physical and chemical properties as well as the sizing technique are described in this paper. Experience of more than 20 paper mills shows that the consumption of maleated rosins in the manufacturing of different types of paper was 20~50% less than the consumption of the natural rosin. Remarkable results and progress have been made in recent years in the studies of a series of maleic type rosins, such as maleated rosin made from ma-leic acid instead of maleic anhydride, paste maleated rosin size, powder maleated rosin size and dispersed rosin size. Fundamental theories concerned have also been preliminarily explored.