The use of petroleum sourced fuels in the past years which make great contribution to the accumulation of carbon dioxide should be replaced by other renewable energy sources.Biodiesel refers to be the best replacement that doesnt cause environmental damage like the fossil fuels used to be.Biodiesel from oil crops, animal fat or even the waste cooking oil from restaurant cant satisfy the realistic demand for fuel.And these sources also have other problems like the need of cultivated fields for oil crops, unstable source of waste cooking oil and so on.Microalgae seem to be the only source of renewable biodiesel that is capable of approaching the global demand for transport fuels.Biodiesel from microalgae biomass has the potential for high volume, cost effective production.Microalgae dont take the farming land and can be produced on relatively small areas of marine or lakes.The productivity of biodiesel from microalgae greatly exceeds the productivity of the best oil crops.Using the microalgae as raw material of biodiesel makes it economically competitive with the original diesel.