The structural change of water clusters of distilled water induced by tourmaline addition was observed and a bacterium Rhodopseudomonas palustris was used to investigate the effects of tourmaline addition on the dehydrogenase activity of the microorganism. The results showed that tourmaline reduced O-17 NMR full width at half maximum intensity (FWHM) for distilled water and the volume of clusters of water molecules. The dehydrogenase activity was improved and remained stable within the pH range from 5 to 11 when tourmaline was added. The results showed that tourmaline controlled the pH of different initial values between 5 and 11 all to about 8.0. Besides the structural change of water clusters, the promoted activity of dehydrogenase observed in this study may be caused by pH self-control by tourmaline. This study provided useful information for the application of tourmaline addition in biological processes such as wastewater treatment. (C) 2005 Elsevier Ltd. All rights reserved.