Paclobutrazol (PBZ) is a growth regulator that widely used in horticulture and in the tomato seedling growth to compact the shoots, increase the stem diameter and, root biomass, allowing more tolerance of the seedlings against adverse weather conditions. The objective of this work was to evaluate the rates of paclobutrazol (0, 4, 7, 10 and 13 mg L-1) applied 15 days after sowing by foliar spray on the growth, chemical composition and xylem vessel number of tomato seedlings cultivated in two periods. The PBZ regardless of the application rate reduced the height of tomato seedlings in both growth periods. The basal stem diameter and leaf area were increased with 13 mg L-1 of PBZ. The lignin percentage also increased with 10 and 13 mg L-1 of PBZ as compared to control for both periods. The number of xylem vessel was not affected by PBZ application on the seedlings in the first period. PBZ application at rates of 7 and 10 mg L-1 increased the xylem vessel number in the second period. In general, the application of 13 mg L-1 of PBZ generated seedling more robust to overcome climate adversities.