PROBLEM TO BE SOLVED: To provide a polyether-modified siloxane having excellent thickening properties for aqueous liquid.SOLUTION: The present invention provides a polyether-modified siloxane represented by formula (1), with the ratio of a molecular weight of Sx-(CH)CO moiety/a molecular weight of O(CHO)(CHO)moiety being 0.12 or less； and a thickener for aqueous liquid having the polyether-modified siloxane. Sx-(CH)COO-(CHO)-(CHO)-CO(CH)-Sx (1) (n is an integer of 50-10000； s is an integer satisfying 0≤s≤n/50； each Sx independently represents a straight-chain/side-chain organo (poly) siloxanyl group).SELECTED DRAWING: None【課題】水性液体に対する増粘性に優れるポリエーテル変性シロキサンの提供。【解決手段】式（１）で表され、Ｓｘ－（ＣＨ２）ａＣＯ部分の分子量／Ｏ（Ｃ２Ｈ４Ｏ）ｎ（Ｃ３Ｈ６Ｏ）ｓ部分の分子量の比が０．１２以下である、ポリエーテル変性シロキサン。前記ポリエーテル変性シロキサンを有する水性液体用増粘剤。Ｓｘ－（ＣＨ２）ａＣＯＯ－（Ｃ２Ｈ４Ｏ）ｎ－（Ｃ３Ｈ６Ｏ）ｓ－ＣＯ（ＣＨ２）ａ－Ｓｘ・・・（１）（ｎは５０～１００００の整数；ｓは０≦ｓ≦ｎ／５０を満たす整数；Ｓｘは各々独立に直鎖／側着のオルガノ（ポリ）シロキサニル基）【選択図】なし
