Abstract: The young trees of potted Ulmus parvifolia were treated with paclobutrazol (PP333). The effects of PP333 on the plant growth were obvious, and the after-effects were also very distinct. Within the concentration of PP333 100~200 ppm, there showed the inhibition of the growth of shoots, crowns and leaf area, but the leaf thickness and the content of chlorophyll were increased. PP333 also caused the decrease of the content of IAA and the increase of ABA in the leaves. During the leaf growth and development, the plate meristem and marginal meristem were inhibited by PP333, but it could increase the thickness of palisade tissue, spongy tissue and epidermis. All these effects greatly improved the enjoying value of the potted Ulmus parvifolia.