A polymer comprises recurring units of formula (1) and recurring units having acid labile groups which units increase alkali solubility as a result of the acid labile groups being decomposed under the action of acid, and has a Mw of 1,000-500,000. R1 and R2 each are hydrogen, hydroxyl, hydroxyalkyl, alkyl, alkoxy or halogen, and n is 0, 1, 2, 3 or 4. The polymer is useful as a base resin to form a chemically amplified, positive resist composition which has advantages including a significantly enhanced contrast of alkali dissolution rate before and after exposure, high sensitivity, high resolution, and high etching resistance and is best suited as a micropatterning material for use in VLSI manufacture.