Among a large number of factors which influence the success of the overall lithographic process, the photoresist performance is a central one. Particularly, the polymer in a photoresist which undergo crosslinking or chain scission when irradiated with an energy such as UV, X-ray and electron beam, play key roles in the resist performance. Therefore, two most conventional photoresists, OMR-83 as a negative two component photoresist and AZ-1370 as a positive two component photoresist were chosen to study. After separation of base polymers from the resists by successive fractional fractional precipitation method, average molecular weight, molecular weight distribution, temperature(Tg), cyclicity and structure of base polymers were characterized