A .beta.-glucan-containing fat and oil composition contains .beta.-glucan of microorganism origin or basidiomycete origin. The .beta.-glucan-containing fat and oil composition has .beta.-glucan uniformly dispersed in a food without worsening the texture, taste etc. of the food. The novel microorganism can efficiently produce .beta.-glucan which has a high activity and favorable qualities as .beta.-glucan of microorganism origin as described above from less expensive saccharides such as sucrose at a high production speed.