The transesterification of vegetable oils into Biodiesel at 60℃ was performed on the rotary viscometer. The overall yield(%) of fatty acid methyl ester from canola oil at optimum conditions was 95%. The viscosities of fatty acid methyl esters were predicted by Orrick and Erbarr's model. The overall yield increased as the viscosities of fatty acid methyl esters decreased. The limiting molar ratio of methanol to oil appeared to be 1:5. The content of sodium hydroxide as the optimum catalyst appeared to be 0.5wt%.