Abstract: A tubular polymerization reactor comprising a feed opening for a polymerizable material at one end portion, a withdrawal opening for the resultant polymer at the other end portion, a tubular reaction space within the reactor extending from said feed opening to said withdrawal opening, and a rotary conveying member disposed within the reaction space and extending therealong with some clearance from the inner wall surface of the polymerization reactor; characterized in that(i) the length-to-diameter ratio of the tubular reaction space is about 20 or more, and(ii) the rotary conveying member is of a tubular coil-like shape;and a process for polymerization using the aforesaid tubular polymerization reactor.