The present invention provides a solution to a problem that a composition including a reactive silicon group-containing polyether undergoes red coloration. More specifically, in a reactive silicon group-containing organic polymer which contains Co, the problem concerned is solved by limiting the Co content to 0.5 ppm or less. As the reactive silicon group-containing organic polymer, for example, a reactive silicon group-containing polyether (A) or a mixture of the reactive silicon group-containing polyether (A) and a vinyl polymer (B) may be cited. The reactive silicon group-containing polyether (A) is obtained, for example, by reacting a polyether or a derivative thereof which contains Co in a content of 0.5 ppm or less with a silane compound which has a group capable of reacting with the polyether or the derivative thereof and has a hydrolyzable group.