PURPOSE: To obtain an integrated composite membrane having good structural maintainability and a high bubbling point, and reusable by washing by forming an asymmetric polysulfone ultrafiltration membrane integratedly with a preformed non-fibrous microporous membrane made from a specified base- resistant polymer on the microporous membrane.

CONSTITUTION: This composite ultrafiltration membrane comprises a microporous base-resistant membrane support made of a microporous non-fibrous polyolefin or sulfone polymer and an ultrafiltration layer combined to the support and covered with a skin made of sulfone polymer as a multilayer composite produced by applying a sulfone polymer solution to the support of the microporous polyolefin or sulfone polymer by uniformly controlled thickness and then depositing the sulfone polymer to form the porous ultrafiltration layer. As a result, this membrane is resistant to the deterioration caused by contact with strong alkali and reusable by washing.