Abstract: The effects of four plant growth regulators, S₃₃₀₇, Pix, PP₃₃₃ and CCC (three spraying concentrations:100, 150 and 200 mg·kg^-1) on the growth, development and physiological characteristics of tobacco seedlings transplanted in straw-made pots and plastic trays were studied in field during 4-leaf to 5-leaf stage.The results showed that the root vigor of seedling was significantly improved, the chlorophyll content, stalk thickness and fresh weight were increased, the resistance of plants was enhanced by spraying PP₃₃₃ at 150 mg·kg^-1 or Pix at 200 mg·kg^-1.