A new piperidine derivative represented by the formula: ##STR1## wherein X is oxygen, sulfur, carbonyl, hydroxymethylene or methylene; R is straight-chain alkylene having 1-4 carbon atoms with or without lower alkyl substituent(s); m and n are 0 or 1, and are different from each other (i.e., both m and n are not 0 or 1); and (D).sub.m', R.sup.1 and (R.sup.2)n' are usually used as substituents, has a hypotensive activity.