Abstract: Soil pot and water culture experiments of two tobacco genotypes of different Cd accumulating patter,N.tabacum(K326) and N.rustica,were carried out to study their difference in total and individual contents of low molecular weight organic acids(LMWOA) in the exudates of root system.The results showed that:1) In soil pot experiment,tobacco seedling growth was promoted by Cd treatment at the rate of 1 mg/kg,while it was seriously inhibited at Cd rate of 10 mg/kg.N.rustica was more tolerant to Cd than was K326.2) In soil pot and water culture experiments,LMWOAs secretion was promoted at low Cd level,it was inhibited at high Cd level.Total amount of LMWOAs exudates by N.rustica was higher than that by K326,which indicated that higher LMWOAs exudation might be one of the major factors leading to higher tolerance of N.rustica to Cd.3) The contents of oxalic acid,tartaric acid,methanoic acid and lactic acid were higher in N.rustica than in K326,however,the proportions of the four organic acids in total organic acids were not significantly different between the two genotypes;the different tolerance to Cd of the two genotypes probably related to the amounts of the four organic acids,rather than the proportion of each organic acid.