Tung oil modified rosins (TR) were prepared by reaction rosin with different amount of tung oil via Diels-Alder addition reaction and further used in the formulation of glycerin ester of tung oil modified rosins (GTR) with flexible characteristics. The effects of the amount of tung oil on the bromine value, molecular weight, thermostability, physical, and tackifying properties of GTRs were studied. The results showed that the bromine value of GTRs decreased and molecular weight of GTRs increased with the increase in the amount of tung oil. Meanwhile, increasing the amount of tung oil resulted in a significant decrease in both the softening points and viscosities of GTRs, but a slight increase in the thermostability of GTRs due to the incorporation of the flexible fatty chains into the rigid hydrophenanthrene units in rosins. Applied in PU adhesive as tackifier, the increase of the flexible chains content in GTRs led to an increase first and then decrease in both the miscibility of GTRs with PU and the T-peel strength of adhesives. The elongation at break of films increased monotonously, but their tensile strengths increased first and then decreased with increasing the flexible chains content in GTRs. GTRs with desired properties were prepared when the tung oil/rosin weight ratios were in the range from10/100 to 40/100. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1700-1706, 2013