This paper deals with the causes of the high crystallizing tendency of the rosin from Finus mossoniana; the relationships between the crystallizing tendency, the pine species and the resin acid composition; and the method of inhibiting the crystallizing tendency of rosin. The experiments concerned were carried out in a series of changes of the contents of certain resin acids of rosin. The crystallizing tendency of rosin was determined by the Palkin-Smith’s method (rosin: acetone = 1:1) which is internationally commonly used. Results of the study can be summed up as follows:1 . Both the oleoresin and rosin from Pinus mossoniana have high contents of abietic-type resin acids (over 70%) which lead to high crystallizing tendency of rosin.2. Changes in the contents of pimaric-type resin acids and dehydroabietic acid in the rosin of Pinus mossoniana do not make any apparent effect in the decrease of the crystallizing tendency of rosin, whereas the contents of palustric acid and abietic acid do play an important role in decreasing the crystallizing tendency of rosin.3 . When the mixed oleoresin of Pinus mossoniana (60%) and Pinus elliotti (40%) was processed, or when the rosin from p. mossoniana and that from p. elliotti were mixed, both mixed rosins had a good index of crystallizing tendency. The time for the first appearance of crystals was about 2 hours thereafter. Analyses of the contents of palustric acid and abietic acid in the mixed rosin showeed: that their con-tent ratio was in the range of 1:1.10-1.40- : -4 . The rosin from P. elliotti produced in Jian, Jiangxi showed lower crystallizing tendency; the time it took to crystallize was over 2 hours. When pure abietic acid was added to it by over 30% of the volume of the rosin, its crystallizing tend-_ency deteriorated, and crystals of resin acids appear within 15 minutes.