In this paper, modal colloidal substances (MCS)were employed to study the effects of in-process colloid on the properties of newsprint. The adsorption of MCS on fibers and optical and physical properties of newsprint were both investigated with and without retention systems including agglomerating agent and flocculent. Results showed that MCS could be absorbed on the fibers without retention system, and retention systems could promote the MCS retention efficiency while the physical properties of sheets was affected by blocking the formation of hydrogen bonding between fibers and the surface tension of water and density of paper decreased