The present invention discloses a new plant growth regulating composition which comprises, as an active ingredient, a selected succinamide compounds, maleimide compounds, succinic anhydride compounds, maleic anhydride compounds of general formula: ##STR1## if preferably, along with ethephon. In this invention, the plant growth regulating composition has the effect of plant growth controlling activity (herbicidal activity) and an abscission layer forming activity for a fruit harvest aid, and the said plant growth regulating composition does not cause hazards such as defoliation and injuries to the fruit surface, nor does it affect immature fruit, but acts specifically on matured fruit and promptes formation of abscission layer that aids in the separation of matured fruit.