Gel electrophoresis is one of the most common techniques in biotechnology, which can separate DNA samples (e.g. PCR products) according to their molecular sizes under an electric field, and for further analysis and isolation of DNA. This video introduces the method of preparing a piece of agarose gel, setting up an electrophoresis tank for gel electrophoresis, the mixing of DNA loading dye and DNA samples, the loading of the dye-DNA mixture to the wells of the piece of agarose gel, as well as the observation of the result of gel electrophoresis.