During the last two decades, phenolic compounds have become the subject of intense research in the environmental preservation field. Phenols are included on the lists of priority pollutants in many countries and their determination is required. In this work, a fast, sensitive miniaturized whole cell conductometric biosensor was developed for the determination of phenol. The biosensor assembly was prepared by immobilizing Pseudomonas sp. (GSN23) bacteria, from oil refinery contaminated soils, on the surface of gold interdigitated microelectrodes. The results obtained with conductometric measurement allowed sensitive detection of phenol from 1 to 300 mg L-1 (10-3187 mu M), with a detection limit (LOD) of 0.2 mg L-1 (2 mu M). Furthermore, the bacterial biosensor was successfully applied to the determination of phenol in spiked river samples. Capsule abstract: A conductometric bacterial biosensor based on Pseudomonas sp. (GSN23) bacteria, from oil refinery contaminated soils has been developed. The detection limit for phenol is 2 mu M.