This experiment was carried out at International Rice Research Institute (IRRI) farm to investigate the effect of plant growth regulators on lodging in rice and to determine plant characteristics when plant growth regulator applied at different concentrations and different times. The experimental plant growth regulator Hoe 78784 when applied at booting prevented lodging and significantly increased grain of IR 21820-154-3-2-3. However, they did not affect significantly the crop vegetative characteristics and yield component, except by decreasing plant height and internode elongation, and increasing the number of vascular bundles, and the thickness and diameter of the third and fourth internodes. But when applied at 30 DT, it significantly decreased grain yield of all test varieties due to shortened panicle length and increased unfilled spikelet percentage. Hoe 78784 applied at heading did not increase yield nor did it prevent lodging.