An objective of the present invention is to provide DNAs encoding novel plant proteins having a gibberellin (GA) 2-oxidation activity. Another objective is to modify plant height by utilizing these DNAs for regulating the gibberellin content.PCR was performed using degenerate primers, and novel OsGA2ox2 and OsGA2ox3 genes were obtained. The present inventors discovered that unlike products of other GA2-oxidases such as OsGA2ox1, the product of OsGA2ox3 catalyzes the two-step oxidation of GA.sub.20 to GA.sub.29 and then of GA.sub.29 to GA.sub.29-catabolite. In addition, the present inventors also found that the growth of the transgenic rice plants expressing OsGA2ox3 was suppressed as compared to control plants.