This paper describes a solution-phase approach to the synthesis of selenium nanoparticles by reducing selenious acid solution with ascorbic acid in the presence of polysaccharides, such as chitosan (CTS), konjac glucomannan (KGM), acacia gum (ACG), and carboxymethyl cellulose (CMC) etc. The monodispersed spherical selenium colloid particles obtained were very stable in solution. The influences of temperature and ultrasonic on the morphology of selenium nanoparticles were also discussed.