This study was carried out to determine the optimal dosage of a plant growth regulator, uniconazole, for controlling the growth of Syzygium campanulatum for container planting purposes. Uniconazole at ascending rates of 0, 10, 20, and 30 mgl^-1 was applied as soil drench to plants grown in polyethylene bags (33 x 27 cm). The application of uniconazole significantly inhibited vegetative growth in terms of height and leaf area. Meanwhile, the most effective application rate of uniconazole for height suppression was 10 mgl^-1. The transpiration rate and stomatal conductance of the plants, treated with 30 mgl^-1, were slightly lower as compared to the control plants, while the photosynthetic rate was not affected. However, the chlorophyll fluorescence measurement indicated that the application of uniconazole did not affect the photosynthetic performance of this particular species. Uniconazole was able to extend the trimming cycle and would be very helpful in controlling the height of S. campanulatum without affecting the physiological processes in the plant.