Recently, the world is facing a vital calamity in respect to energy and environment.Biodiesel is considered to be a most sustainable alternative to conventional fuels as being renewable and environment-friendly.Microalgae is currently being thought as an ideal third generation biofuel feedstock because of their rapid growth rate, high production capacity of lipids and not competing with food or feed crops.In present work, modified alumina support with high specific surface area was prepared by simple peptization method, and supported catalysts with different KOH content were prepared.The conversion of microalgae oil to biodiesel was investigated.Figure la reveals that as the KOH loading amount increasing from 5 to 25wt%, the oil conversion increases from 83.3% to 97.7%, and the highest oil conversion (97.7%) is obtained at 25wt% KOH amount.However,when the amount of KOH is over 25wt%, the oil conversion decreased gradually.According to the results of GC-MS(Figure lb), the components of biodiesel in present work are mainly methyl esters of C14∶0, C16∶0,C20∶4, C22∶6.According to BET、 SEM and XRD results, a new phase Al-O-K compound is active phase for oil conversion, and the agglomeration and change of pore structure should be the main reasons for activity decrease when KOH content higher than 30wt%.