A strain of Penicillium citreoviride was screened from soil to produce exo-isomaltotriodextranase,which specifically released isomaltotriose as main products from dextran T70.The optimum condition for Isomaltotriodextranase production consisted of 1 % starch,1 % dextran,0.1 % NH4Cl and 0.1 % yeast extract,the initial pH for 6.0,1 % inoculating quantity,rate of shaking flask with 50 mL liquid in a 250 mL flask was 120 r/min.After fermentation for 13 days at 25℃,the enzyme activity was 176.80 U/mL.The enzyme displayed maximum activity at 55℃.The half-life of the enzyme was 3 h at 50℃.The optimum pH was pH 6.5,and the enzyme activity was stable from pH4.0～6.5.The enzyme was enhanced by K + and Ba2 +,but was inhibited by Ca2 +,Fe2 +.The enzyme activity could be improved by the ionic strength of NaCl at 150 mmol/L.