Abstract: The room temperature-curable polymeric composition is prepared by admixing (a) a polyether terminated at both molecular chain ends each with a mercapto group with (b) a 3-methacryloxypropyl silane having at least two hydrolyzable groups, e.g. alkoxy groups, in a molecule and (c) a 1,1,3,3-tetramethyl guanidino-containing organosilicon compound. The component (b) first reacts with the mercapto group of the component (a) to introduce silicon-bonded hydrolyzable groups to the molecular chain ends of the polyether and the silicon-bonded hydrolyzable groups pertain to the crosslinking reaction with the atmospheric moisture. The composition has good storability and workability and is capable of giving a cured rubbery elastomer without the addition of a toxic lead compound as a curing catalyst which is indispensable in the conventional polyether-based room temperature-curable polymeric compositions.