Biodiesel, an alternative diesel fuel derived from plant oils, animal fats, or used frying oils, largely consists of the mono-alkyl esters of the fatty acids comprising these feedstocks. This work investigates the production of fatty acid methyl esters or biodiesel from non-edible oils like ailanthus and beech oils in sub-and supercritical methanol. Mostly, biodiesel is derived from the vegetable oils using NaOH or KOH catalytic transesterification (m) ethanol process. Soxhlet and supercritical fluid extracts of freshly cut ailanthus (Ailanthus altissima) and beech (Fagus orientalis) have been obtained using acetone. While the average yields of the Soxhlet extracts were 2.7 and 2.5%, the average yields of the supercritical acetone extracts obtained at 513 K and 6.5 MPa were 10.4 and 9.6%, respectively. The wood oils were transesterified at 1:1, 1:20, and 1:41 oil-methanol molar ratios in sub-(at 503 K) and supercritical (at 518 and 563 K) conditions. It was observed that an increase in temperature and in oil to methanol molar ratio improved the reaction conversion.