The present invention relates to a plant growth regulator comprising as an active ingredient an epoxycyclohexane derivative represented by general formula (1): ##STR1## wherein R.sup.1 is a hydrogen atom, a C.sub.1 -C.sub.6 alkyl group or C.sub.3 -C.sub.6 cycloalkyl group, and R.sup.2 and R.sup.3 are independently C.sub.1 -C.sub.6 alkyl groups or are combined to form a C.sub.2 -C.sub.3 polymethylene group which may be substituted with a C.sub.1 -C.sub.6 alkyl group, as well as to a plant growth regulator comprising the epoxycyclohexane derivative and a brassinosteroid as active ingredients. The epoxycyclohexane derivatives exhibit a potent plant growth regulating action which is equivalent to or higher than that of abscisic acid, and are useful as plant growth regulators such as a plant growth accelerator, a germination growth accelerator, a transpiration and wilting inhibitor, a cold resistance enhancer, an accelerator for growing, thickening or maturing fruits, roots, stems or bulbs, etc. A synergistic effect is achieved by combination of the epoxycyclohexane derivative with a brassinosteroid.