Modified phenolics can have a retarding effect on the gelation of wood oil. Modified phenolic resins can be used in media for paint, varnishes, primers, overprinting varnishes, litho, letterpress and rotogravure inks. Varnishes based on rosin phenolic are faster drying, have better durability, are harder and glosser, and have greater resistance to water than ones based on ester gums. These physical properties is concerned with molecular weight distribution of rosin modified phenol resin. This paper was studied about molecular weight distribution of rosin phenolics which where prepared between 130~250C. The results were as follows:1) Average molecular weights increased with increasing reaction temperature. 2) Mw/Mn were from 3.43 to 46.44 with increasing reaction temperature and so the molecular weight distributions were changed from random distribution to broad distribution 3) The relation ship between intrinsic viscosity and weight average molecular weight was follows: [ ]= 1*10 M ,M =M. 4) Esterification reaction between the acid group of rosin and polyol was started about 230°C