Disclosed is an adjustable vertical pipe support, in which a second saw-toothed portion is positioned in a wedge of a length adjusting member for adjusting a length of upper and lower pipes, so as to prevent unlocking or slip of the upper pipe and thus improve the safety of the vertical pipe support, even though a first rotation adjustor is rotated by a tensile force or an external force. The adjustable vertical pipe support includes a wedge with a first and second saw-toothed portion on the inner peripheral surface, in which any one of the first saw-toothed portion and the second saw-toothed portion is inclined upwardly so as to suppress downward movement of the upper pipe, and the other is inclined downwardly or is formed in the shape of a ridge so as to suppress upward movement of the upper pipe.