The present invention provides a copolymer which can prevent problems associated with immersion lithography (including occurrence of a pattern defect such as water mark, and variation in sensitivity or abnormal patterning due to elution of an additive such as a radiation-sensitive acid-generator) and which provides surface characteristics suitable for immersion lithography, and a composition containing the copolymer. The copolymer for immersion lithography has, at least, a repeating unit (A) that generates an alkali-soluble group by removing protecting group through action of an acid, and a repeating unit (B) having a lactone structure, wherein, when a solution of the copolymer in propylene glycol monomethyl ether acetate (hereinafter may be abbreviated as "PGMEA") is applied to a wafer and then heated to form a thin film, and a 15-.mu.L droplet of pure water is added onto the thin film, the inclination of the wafer at the time when the water droplet starts to move is 35.degree. or less, or the contact angle of the top edge of the water droplet at the time when the water droplet starts to move is 64.degree. or more.