Three different molecular weights of chitosan oligosaccharide (COS) were explored as draw agents in the forward osmosis (FO) process. The physical properties such as pH, conductivity, viscosity and osmotic pressure were investigated. The change regularity of water flux, reverse solute flux, rejection rate in the FO processes under different molecular weights, different concentrations and different membrane orientations were explored. Water recovery rates were also evaluated. The results showed that their characteristics of high conductivity and high osmotic pressure can provide favorable FO performance. The water flux of AL?DS mode is higher than that of AL?FS mode and reverse solute flux of AL?DS mode is also slightly higher than that of AL?FS mode. The rejection rates are both over 99.9% in the two membrane orientations. Moreover, rejection rate of AL?FS mode is slightly higher than that of AL?DS mode. Water recovery rates of draw solutions also exhibit good performance under different concentrations of COS as draw agents.Key words: forward osmosis; draw solution; chitosan oligosaccharide