The physical and chemical properties of alfalfa mosaic virus from white clover have been studied by analytical ultra-centrifuge. The results showed that this virus sample contains five different components which possess the S_(20) values of 98s, 82s, 72s, 65s, and 36s respectively. While measured the S values we have used schlieren light system by using UV system as control. The twice changed speed method also has been used to measure the S values at different concentration of samples under different ion strength.