Results of a study on cultivation of Aspergillus oryzae and amylase production in a new kind of fermenter are presented. A new rotary draft tube fermenter (RTF) which has a rotating draft tube with a helical ribbon was developed for high viscous culture broth fermentation. The mixing time was shorter in the RTF than in reactors equipped with turbine impellers. Fed-batch cultivation of A. oryzae with maltose as the sugar source produced more amylase than batch culture. Maximum specific glucoamylase production rate was obtained when the specific glucose consumption rate was 0.015 g-glucose/g-cell per hour. The final cell, a-amylase, and glucoamylase with the RTF were 30 g/l, 83,400 U/ml and 1.53 U/ml, respectively.