Abstract: An object of the present invention is to provide a novel plant growth inhibiting agent and a plant growth inhibiting method using the same. The plant growth inhibiting agent of the present invention comprises, as an active ingredient, a compound represented by the following formula (I?) and/or a salt thereof. In the formula (I?), R1a represents a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C14 aryl group, a substituted or unsubstituted C3 to C13 heteroaryl group, or the like; R2 represents a substituted or unsubstituted C1 to C20 alkylene group, a substituted or unsubstituted C6 to C14 arylene group, or the like; R3a represents OH, a substituted or unsubstituted C1 to C6 alkoxy group, or the like; X represents an oxygen atom; Y represents a substituent; q represents any integer of 0 to 3; n represents 0 or 1; and m represents 0 or 1.