To determine the effects of pH, salinity and temperature on the Cu and Pb biosorption capacities of the subtropical estuarine bacteria Bacillus thioparans strain U3, batch experiments were performed under a variety of laboratory conditions. Of the eight kinetic models employed, the pseudo-second order (PSO) model provided the best fit for the experimental data for both metals. The optimal conditions for Cu biosorption were at pH 6 and 25 °C, while Pb biosorption was maximised at pH 4 and 35 °C. Zero salinity was optimal for both metals. The experimental data fit the Langmuir adsorption model well. The maximum Cu and Pb biosorption capacities of B. thioparans U3 suggest that the bacterium can be a suitable biosorbent for these metals.