NOVELTY - Methanol and oil having high acid number are reacted in the presence of activated carbon carrying sulfuric acid catalyst. The residual methanol and residual activated carbon carrying sulfuric acid catalyst are recycled, and liquid reactant is separated. Then, methanol and obtained liquid reactant are reacted in the presence of potassium hydroxide, heated and left undisturbed, to form layers containing methanol, bio-diesel oil, glycerine, potassium hydroxide and soap. Then, the methanol from layer is recycled, washed and refined, to obtain bio-diesel oil.    USE - Manufacture of bio-diesel oil.    ADVANTAGE - The method easily provides environmental friendly bio-diesel oil having excellent recyclability.    DETAILED DESCRIPTION - Activated carbon grains (2-6 times) are dried using sulfuric acid (40-80%), left for 24 hours, filtered by pumping, washed with distilled water for 2-3 times, fed into oven and dried, to obtain activated carbon carrying sulphuric acid catalyst having active carbon (43.5-74.9 weight%) and sulfuric acid (25.1-56.5 weight%). Then, methanol and oil having high acid number in the mol ratio of 6:1-14:1 are reacted in a reactor in the presence of activated carbon carrying sulfuric acid catalyst (2.5-3.5 weight% with respect to oil) and heated at 80-95 degrees C for 0.5-3 hours in water bath. Then, residual methanol and activated carbon carrying sulfuric acid catalyst are recycled by atmospheric distillation and the liquid reactant is separated. Then, methanol and obtained liquid reactant in the mole ratio of 3:1-9:1 are reacted in another reactor in the presence of potassium hydroxide (0.5-1.2 weight% with respect to oil) heated in water bath at 40-70 degrees C, condensed, stirred for 0.5-1 hour and left undisturbed, to form layers, in which the upper layer is mixture of methanol and bio-diesel oil, and the lower layer is mixture of glycerine, potassium hydroxide, soap and methanol. Then, the methanol from upper layer is recycled by atmospheric distillation, washed using hot water at 65-95 degrees C for 2-3 times and refined by vacuum distillation, to obtain refined bio-diesel oil.