NOVELTY - Preparing biodiesel by using amino acid ionic liquid for catalyzing hydrolysis of castor oil, comprises adding castor oil, methanol and amino acid ionic liquid into a flask provided with an e.g. blender, starting the blender and an oil bath, monitoring the time at which the temperature is increased to the reflux temperature, retaining the process to normal pressure, determining glycerol content, transferring the reaction liquid to a liquid distribution funnel, allowing to stand, where the upper layer is crude biodiesel phase and the lower layer is amino acid ionic liquid phase and separating.    USE - The method is useful for preparing biodiesel by using amino acid ionic liquid for catalyzing hydrolysis of castor oil.    ADVANTAGE - The method: produces high yield of glycerol whose average yield is more than 84% and produces the product with high methyl ester content (more than 87 wt.%); utilizes the catalyst which can be recycled for several times; is economical and ecofriendly; and conserves energy.    DETAILED DESCRIPTION - Preparing biodiesel by using amino acid ionic liquid for catalyzing hydrolysis of castor oil, comprises adding castor oil, methanol and amino acid ionic liquid into a pre-dried three-port flask provided with an electric blender, a reflux condensation pipe and a thermometer, starting the blender and a constant-temperature oil bath, monitoring the time at which the temperature is increased to the reflux temperature at normal pressure, retaining the integral reaction process to normal pressure, determining the content of glycerol obtained to detect the yield at different reaction intervals, transferring the reaction liquid to a liquid distribution funnel, allowing to stand, where the upper layer is crude biodiesel phase (mixture of methyl ester and methanol) and the lower layer is amino acid ionic liquid phase (mixture of ionic liquid, methanol and glycerol), separating, distilling the crude biodiesel for removing excess methanol to obtain the biodiesel product, distilling the ionic liquid phase under normal pressure and depressurizing to remove methanol and glycerol and recycling the purified amino acid ionic liquid.