An agent, which is a surface-treating agent comprising at least one perfluoro(poly)ether group containing silane compound of any of the formulae,,,, and: (R f - PFPE) β' - X 5 - (SiR 1 n,R 2 3-n) β ··· (R 2 3-n R 1 n Si) β - X 5 - PFPE-X 5 - (SiR 1 n R 23-n) β ··· (Rf-PFPE) γ' -X 7 - (SiR a k R b l R c m) γ ··· (R c m R b l R a k Si) γ - X 7 - PFPE - X 7 - (SiR a k R b l R c m) γ ··· wherein: PFPE each independently is: -(OC 4 F 8) a -(OC 3 F 6) b -(OC 2 F 4) c -(OCF 2) d - wherein a, b, c and d are each independently an integer of 0-200 and (a+b+c+d) ≥ 1, and the order of the respective repeating units in parentheses with the subscript a, b, c or d is not limited; Rf each independently is C 1-16 -alkyl optionally substituted by one or more F; R 1 each independently is H or C 1-22 -alkyl; R 2 each independently is hydroxyl or a hydrolyzable group and there is at least one R 2 in the formulae,, and; R 11 each independently is H or halogen; R 12 each independently is H or an alkyl group having 1-20 carbon atoms; n is, independently per (-SiR 1 n R 2 3-n) unit, an integer of 0-3; X 1 is each independently a single bond or a 2-10 valent organic group; X 2 each independently is a single bond or a divalent organic group; t each independently is an integer of 1-10; α each independently is an integer of 1-9; α' each independently is an integer of 1-9; X 5 each independently is a single bond or a 2-10 valent organic group; β each independently is an integer of 1-9; β' each independently is an integer of 1-9; X 7 each independently is a single bond or a 2-10 valent organic group; γ each independently is an integer of 1-9; γ' each independently is an integer of 1-9; R a each independently is -Z-SiR 71 p R 72 q R 73 r; wherein Z each independently is O or a divalent organic group; R 71 each independently is R a' and is defined as R a; R 72 each independently is OH or a hydrolyzable group; R 73 each independently is H or an alkyl group having 1-20 carbon atoms; p each independently is an integer of 0-3; q each independently is an integer of 0-3; r each independently is an integer of 0-3; the number of Si atoms in R a which are straightly linked via the Z group is ≤ five; and in one R a (p+q+r) = 3, and there is at least one R 72 in formula and; R b each independently is OH or a hydrolyzable group; R c each independently is H or an alkyl group having 1-20 carbon atoms; k each independently is an integer of 1-3; 1 each independently is an integer of 0-2; m each independently is an integer of 0-2; and (k+l+m) = 3 in each unit in parentheses with the subscript γ, wherein in the perfluoro(poly)ether group containing silane compounds of any of the above general formulae the proportion of compounds having a molecular weight of ≤ 3,000 or less is ≤ 9 mol-% as measured by Gel Permeation Chromatography analysis; and wherein the number average molecular weight of the perfluoro(poly)ether group containing silane compound is 10,000 or less as measured by GPC analysis. PFPE each independently is: -(OC 4 F 8) a -(OC 3 F 6) b -(OC 2 F 4) c -(OCF 2) d - wherein a, b, c and d are each independently an integer of 0-200 and (a+b+c+d) ≥ 1, and the order of the respective repeating units in parentheses with the subscript a, b, c or d is not limited; Rf each independently is C 1-16 -alkyl optionally substituted by one or more F; R 1 each independently is H or C 1-22 -alkyl; R 2 each independently is hydroxyl or a hydrolyzable group and there is at least one R 2 in the formulae,, and; R 11 each independently is H or halogen; R 12 each independently is H or an alkyl group having 1-20 carbon atoms; n is, independently per (-SiR 1 n R 2 3-n) unit, an integer of 0-3; X 1 is each independently a single bond or a 2-10 valent organic group; X 2 each independently is a single bond or a divalent organic group; t each independently is an integer of 1-10; α each independently is an integer of 1-9; α' each independently is an integer of 1-9; X 5 each independently is a single bond or a 2-10 valent organic group; β each independently is an integer of 1-9; β' each independently is an integer of 1-9; X 7 each independently is a single bond or a 2-10 valent organic group; γ each independently is an integer of 1-9; γ' each independently is an integer of 1-9; R a each independently is -Z-SiR 71 p R 72 q R 73 r; wherein Z each independently is O or a divalent organic group; R 71 each independently is R a' and is defined as R a; R 72 each independently is OH or a hydrolyzable group; R 73 each independently is H or an alkyl group having 1-20 carbon atoms; p each independently is an integer of 0-3; q each independently is an integer of 0-3; r each independently is an integer of 0-3; the number of Si atoms in R a which are straightly linked via the Z group is ≤ five; and in one R a (p+q+r) = 3, and there is at least one R 72 in formula and; R b each independently is OH or a hydrolyzable group; R c each independently is H or an alkyl group having 1-20 carbon atoms; k each independently is an integer of 1-3; 1 each independently is an integer of 0-2; m each independently is an integer of 0-2; and (k+l+m) = 3 in each unit in parentheses with the subscript γ,