Extraction of betulinic acid from leaves of Vitex Negundo Linn was carried out in a series of solvents (methanol, ethanol, isopropyl alcohol, and water). Methanol gave maximum yield of extraction and therefore was used to investigate influence of particle size, speed of agitation, solid loading, and temperature, etc., on the rate and recovery in a stirred batch reactor. Effective intra-particle diffusivity of the acid in each solvent at different temperatures was estimated using an unsteady state mass diffusion model. The diffusivity of betulinic acid through the cellulose matrix of leaves is in the range 1.7 x 10(-13) to 9.23 x 10(-11) m(2)/sec and is strongly influenced by the temperature of the extraction. The Response Surface Methodology was used to estimate optimal conditions for betulinic acid extraction.