Abstract: Microspore embryogenesis system of tobacco(Nicotiana tabacum L.) was employed in the experiments,which offered excellent material of embryos at different stages for the test of auxin treatments.When treated with exogenous auxin of diverse concentrations,1 μmol/L,(3 μmol/L),10 μmol/L of IAA,embryos at early and later stages showed different responses.Auxin enhanced the formation of 2-3 cell embryos and early globular embryos,but inhibited the formation of later globular embryos and the embryo differentiation.The experiments revealed that two phase,early and later,of embryogenesis showed different sensitivity to auxin treatment,which reflects different mechanism of auxin regulation in those two developmental processes.