Abstract A multistage bioreactor consisting of organic ultrathin layers was successfully realized by immobilizing glucose oxidase and glucoamylase by the Langmuir–Blodgett technique (LB technique). Starch as the substrate was quickly converted into gluconic acid and hydrogen peroxide as the products in this bioreactor via the intermediate, glucose. The rate of the sequential reactions was electrochemically measured. This rate increased proportionally with increasing the concentration of starch, and also increased with increasing the amount of glucose oxidase in the LB film. This bioreactor, however, decayed soon. The reason of this decay was considered to be the structural conversion of the LB layers with glucoamylase. The multistage bioreactor constructed by the LB technique will be used not only as a super small-sized, rapid bioreactor or biosensor but also as an investigating means of the reconstitution of membrane enzyme and biomembrane.