Ethylene glycol, sorbitol and glycerol were used as water activity depressors to study the effect of water activity on pectinase production by Aspergillus niger CH4. Ethylene glycol depressed a(W) without supporting growth nor strongly affecting pectinase production in petri dish cultures. This depressor was used to evaluate the influence of water activity on exo-pectinase production by SSF. It was found that although pectinase production decreased at low a(W) values, this activity was present at a(W) values as low as 0.90. The specific activity increased up to 4.5 fold by reducing a(W) from 0.98 to 0.90. The reducing groups accumulated extracellularly suggesting sugar transport limitation as a consequence of a(W) depression.