Abstract: A process for regenerating an adsorbent having adsorbed hardly decomposable substances. The process comprises decomposing the hardly decomposable substances by bringing the substances into contact with a microorganisms and/or an enzyme at an inside or a peripheral portion of pores of the adsorbent. The adsorbent can be regenerated by decomposing and removing the adsorbed substances which are hardly decomposable and harmful to living organisms, such as bisphenols, safely from the adsorbent without adverse effects on the environment such as the secondary pollution.