A liquid sealing agent used for automobile parts, electric parts, various kinds of machine parts and the like exhibits good oil resistance, heat resistance, adhesiveness and flexibility. A vinyl polymer has at least one crosslinkable silyl group and can yield a cured product exhibiting an oil resistance superior to that of a cured product from a reference polymer obtained by replacing the repeating unit thereof with butyl acrylate alone, in any one item of the immersion test according to JIS K 6258 for the land use 3-5 lubricating oil specified in JIS K 2215.