A thorough study on the preparation and application of maleated rosin for paper sizing was formerly carried out and made public in Zhongguo Linye Kexue, (Scientia Silvae Sinicae) No. 2, 1978. The purpose of this article is to search for other maleic and fumaric adducts instead of maleic anhydride for paper sizing. 2, 3 and 5% of both maleic acid and maleic anhydride adduct mixtures have been examined and the sizing effects of these adduct mixtures were found of little difference. As the cost of maleic acid is much lower than that of maleic anhydride in China, it is technically and commercially feasible today using maleic acid as starting material for manufacturing maleated rosin instead of maleic anhydride. Fumaric acid can also be used in tests as paper sizing.