A fluoropolyether-containing polymer-modified silane having formula (1) is provided wherein Rf is a fluorooxyalkyl or fluorooxyalkylene-containing polymer residue, Y is a divalent to hexavalent hydrocarbon group, R and R′ are C1-C4 alkyl or phenyl, X and X′ are hydroxyl or a hydrolyzable group, n is an integer of 1 to 3, a is an integer of 0 to 3, m is an integer of 1 to 5, and α is 1 or 2. A surface treating agent comprising the silane has storage stability and cures into a water/oil repellent layer having weatherability.