The data on development of highly sensitive and selective conductometric biosensor for determination of heavy metal ions are presented. A differential pair of gold planar thin-film interdigitated electrodes deposited on the ceramic substrate was used as a conductometric transducer. As a bioselective element, the three-enzyme system (invertase, mutarotase, glucose oxidase) immobilized on the transducer surface was more sensitive and selective to heavy metal ions as compared with other enzymatic systems due to summary inhibition effect of three enzymes. The enzymes ratio in mem-brane was chosen experimentally taking into consideration obtaining maximal biosensor sensitivity both to the substrate (sucrose) and to heavy metal ions. The optimum time of the biosensor incubation in solution of toxic compounds, required to ensure necessary sensitivity was determined to be 30 min. The calibration curves for determination of different heavy metal ions were obtained. The biosensor selectivity to other groups of toxins was studied too. The biosensor developed is characterized in high sensitivity and selectivity to Hg2+ and Ag+ in comparison with known biosensors for heavy metal ions analysis. Therefore it can be recommended at express analysis of heavy metals in ecological monitoring.