The heterogeneous catalysis of transesterification of gmelina seed oil to biodiesel is evaluated. The oil was extracted from the seeds with n-hexane by solvent extraction and characterized to determine its physiochemical properties. Response surface methodology was applied to optimize the effect of process variables on the biodiesel yield. The base-activated clay catalyst performed as montmorillonite clay with the characteristic property of a Bronsted acid. It has an improved surface area after activation that enhanced its catalytic activity on transesterification reaction. Under optimal conditions, the biodiesel yield was 70.1 %, thus demonstrating that the model predicted well the biodiesel production.