An object of the present invention is to provide a fluorooxyalkylene group-containing polymer composition, which yields a coating having excellent adhesior to a substrate, good water- and oil-repellency, a low dynamic friction coefficient, good releasing property, good abrasion resistance and good stain resistance, and to provide a surface treatment agent comprising the same. The present inventors have found that a composition comprising a fluorooxyalkylene group-containing polymer having a fluorinated group and a hydrolyzable group at each terminal and a fluorooxyalkylene group-containing polymer having hydrolyzable groups at both terminals can form a coating which has excellent water- and oil-repellency, a low dynamic friction coefficient, good releasing property, good abrasion resistance, and good stain resistance.