A mono-enzyme amperometric biosensor has been developed for the estimation of galactose in milk and milk products. Galactose oxidase was immobilized with poly(3-hexyl thiophene)/stearic acid (P3HT/SA) on to indium tin-oxide (ITO) coated glass plates using Langmuir-Blodgett (LB) film deposition technique. The immobilized galactose oxidase in P3HT/SA LB films was characterized using Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy. This P3HT/SA/GaO LB film on ITO-coated glass plate was used as working electrode with platinum as reference electrode for development of galactose biosensor. The biosensor shows the linearity 1-4 g/dl galactose. The effect of galactose concentration, pH, temperature, detection limit, response time and stability of the immobilized galactose oxidase in LB films were also studied. The electrode was found stable upto 45 degreesC and has a shelf life of more than 90 days. (C) 2004 Elsevier Ltd. All rights reserved.