In order to find out the basic and general structure common to enzymatic feedback-systems, which are able to maintain the output of whole system at a desired level with rejecting an external perturbation, dynamic characteristics of various enzymatic feedback-systems were studied by means of computer simulation. Under a constant input, an oscillating feedback-system composed of a single large-sized feedback-loop, was found to be relatively unstable for the external perturbation. On the other hand, a non-oscillating feedback-system, which includes several short-sized feedback-loops, had a capability to retain the end product concentration at a constant level against external perturbation. From the results of the simulation, necessary conditions for the basic structure were discussed.