Process for preparing alkylpolyether-substituted mercaptosilanes of the general formula I, (X)m(X′)n(X″)oSi(—R1—SR2)p  (I) and a Hazen colour number of ≦250 mg Pt—Co/L by reacting compounds of the general formula II, (X′)m+n(X″)oSi(—R1—SR2)p  (II) with m equivalents of the compounds of the general formula III, H—O—((CR32)w—O—)vAlk  (III) using a proton-donating co-catalyst and, if desired, a further catalyst, and separating off liberated X′—H from the reaction mixture.