The investigation of Gambier extracts (Uncaria gambier Roxb leaves) as an inhibitor of calcium carbonate scale formation has been carried out using the bottle-roller batch method with the concentration of a growth solution ranging from 0.1 to 0.6 M and at the temperature of 80 degrees C. The data obtained shows that Gambier extracts inhibit the formation of calcium carbonate scale at the various concentrations of the growth solution. The ability of Gambier extracts as an inhibitor of the formation of calcium carbonate scale is around 40-100% in inhibiting the growth rate of CaCO3 scale. This ability depends on the concentration of Gambier extracts added into the growth solution and the concentration of the growth solution as a growth media of CaCO3 seed crystals. (C) 2010 Elsevier By. All rights reserved.