The catalytic activity of precursor dolomite as a heterogeneous catalyst in biodiesel production has been investigated. The dolomitic material is a double calcium and magnesium carbonate, which when calcinated decomposes into CaO and MgO that are highly basic. The materials were characterized by XRD, TG-DTG, CO2-TPD, FTIR, XPS, SEM, and N-2 adsorption/desorption at -196 degrees C. The raw material was activated and used as a catalyst for the transesterification of canola and sunflower oils with methanol. The conversion of canola and sunflower oils to methyl esters was optimized, under different catalyst amount and oil/methanol ratio, and the maximum conversions were: canola (98.81 +/- 0.02 wt.%) and sunflower (96.52 +/- 0.43 wt.%). (C) 2015 Elsevier B.V. All rights reserved.