A sealing device (1) and method for sealing between a chain (2) and a chain pipe (3), said chain for example being an anchor chain on a marine offshore platform or on a ship, and said chain pipe (3) leading for example to a chain locker for onboard storage of the chain in said platform or ship. The sealing device (1) comprises at least two opposing cover lids (7) positioned at the mouth (8) of the chain pipe (3) or an extension collar (7) thereof. The cover lids (7) are movably arranged from an open position into a closed position in which the cover lids (7) abut each other and seal the chain pipe (3) from water intrusion by sealingly engaging a chain link (10) of the chain. Furthermore, the cover lids (7) are provided—in mutual abutment sides (15) thereof—with one or more recesses (16) shaped in conformity with the contacting outer periphery (17) of said chain link (10). The invention is especially characterized in that the cover lids (7) each exhibit at least one inflatable seal element (18), said seal element (18) extending along a respective mutual abutment side (15) of the cover lids (7) and being adapted to expand upon pressurization with a fluid such as pressurized air, into a radial sealing engagement with the chain link (10), and that the cover lids (7) are attached to an extension collar (9) of the chain pipe (3), said extension collar (3) being movably arranged with respect to the rest of the chain pipe (3) by means of a flexible interconnection collar (47) mounted therebetween.