Silicon (Si) is an important element in plant nutrition, although it is not considered an essential element. The role of silicon in leaf growth and hormones responsible for silicon uptake has not yet been determined in tobacco. Burley tobacco ( N. tabacum L. cv. KB 108) seedlings, which were grown in a growth chamber under 12 hour photoperiod (day and night temperatures were kept at 30°C and 20°C, respectively) for 17 days after transplanting, were sprayed with 100 ppm and 200 ppm silicon solution. The shoot samples collected at 6h, 12h, 24h and 48h were analyzed for endogenous gibberellins (GAs), jasmonic acid (JA) and salicylic acid (SA). The GAs and JA contents were measured by GC-MS-SIM, while SA contents were measured by HPLC. Contents of all endogenous GAs in non-C13 and early-C13 hydroxylation pathway were significantly affected by the application of silicon in tobacco seedling shoots. Silicon treatment increased the bioactive GA₄ and GA₁ contents, thus showing an increased non-C13 hydroxylation. However contents of GA₉, a precursor of GA₄ biosynthesis, were not changed significantly. This result suggests that activity of 3ß-hydroxylase, which catalyzes GA₉to GA₄ biosynthetic step, may be up-regulated by the enhanced silicon supply. Compared to the control, JA contents increased from 19% to 25% and SA from 12% to 16% in silicon applied treatments. The foliar application of silicon enhances endogenous growth hormones, thus the disease resistances could be increased in the tobacco plant.