Abstract: A method of preparing a volatile fatty acids (VFAs) is provided. More particularly, the method includes chemically or biologically pretreating a residue of algae to obtain an extract of the algae residue, filtering the extract of the algae residue and anaerobically fermenting the filtrate. The method of preparing VFAs can be used regardless of the kinds of algae, a process of producing VFAs can be simplified since there is no need to develop an enzyme for anaerobic fermentation, and a yield of VFAs can be increased since the VFAs can be produced from different kinds of organic components such as proteins or fats in addition to carbohydrates. Accordingly, the method can be useful in producing VFAs in an economical and efficient manner.