A novel waste water scale-derived catalyst was prepared through calcining the waste water scale and used as an active and stable catalyst for the production of a clean and green alternative fuel-biodiesel via transesterification reaction of soybean oil with methanol. The effect of calcination temperature in range of 200-1000 degrees C on the catalytic activity was investigated. The maximum biodiesel yield reached about 93% under the optimal condition. Acceleration of the catalytic activity of water scale-derived catalyst for biodiesel synthesis was also studied. In addition, the transesterification reaction mechanism was proposed. Operational simplicity, low cost of catalyst used, high yields, wide applicability and reusability are the key features of the waste water scale-derived catalyst. The results suggest that the waste water scale-derived catalyst is a promising catalyst for a green and durable biodiesel production process. (C) 2014 Elsevier Ltd. All rights reserved.