Transesterification of oil to biodiesel was carried out using alkaline catalysis supported by sepiolite - a naturally-porous hydrated magnesium silicate with the highest surface area among all clay minerals. The catalyst particles, prepared by loading 10-50 wt.% of K2CO3 into sepiolite, followed by calcination at 773 K, were found to be very active in the catalysis of the transesterification reaction of canola oil with methanol. The purities of the biodiesel products were assessed via ATR-FTIR and H-1 NMR and found to readily surpass the 96.5% purity requirement of the European EN standard 14103. The biodiesel yield was characterized as a function of the transesterification reaction time, the methanol to oil molar ratio, reaction temperature and catalyst concentration. Methyl ester yields of around 98.5 +/- 0.6% could be obtained using sepiolite supports loaded with 40 and 50 wt.% K2CO3. The testing of the recovered K2CO3(50%)/sepiolite catalyst particles for their reusability and stability indicated that the initial catalytic activity of the catalyst could be maintained for at least five reaction cycles. This unusual maintenance of the activity of sepiolite supported catalysts is possibly associated with the minimization of the leaching of K2O, occurring as a result of the special structure of sepiolite, that is unlike any other clay. (C) 2013 Elsevier B.V. All rights reserved.