An experiment was conducted to obtain the basic information on overgrowth of rice seedling using GA biosynthesis inhibitors such as uniconazo]e and pachlobutrazol. For this. three application times, just before seeding, 1.5 . leaf stage and 2.5 leaf stage, were tested with the different dosages. For shortening effect of plant height, uniconazole had greater effect than pachlobutrazol. The shortening of plant height by plant growth regulators were mainly due to shortening effect of the leaf sheath rather than leaf blade. For soil incorporation treatment, shortening effect was continued until 30 days after seeding while this was decreased thereafter. Early application and high dosage generally resulted in high shortening effect. The ratio of dry weight was decreased by chemical application and the shortening ratio of plant height was positively correlated with the healthy score.