The rheological characteristics of anionic colloidal unimolecular polymer (CUP) particles in water were investigated. the intrinsic viscosities were determined for CUPs with different molecular weights as a function of volume fraction. the specific viscosities were measured and fit with models considering hydrodynamic interaction and electroviscous effects. the rheological characteristics were consistent with a surface layer of water which increases with the particle size or molecular weight of CUPs. the effective charges on the surface of particle were calculated and correlated with the rheological behavior of the CUP particles from the dilute to semidilute range, a volume fraction of 0.0001-0.08.