Polyurethane dispersions(PUD) were prepared from IPDI, PHMCD, DMPA as anionic site, and ADH as end-capping. This prepolymers were dispersed in the aqueous phase by neutralization emulsification. The polyurethane dispersions were electrostatically stabilized with carboxyl group incorporated into their particles, which were neutralized by TEA(triethylamine). The physical properties of aqueous PU prepolymer were investigated by differential scanning calorimetry (DSC), gel permeation chromatography (GPC), dynamic light scattering (DLS), and Rheometer. This procedure contains the effect of molecular weight on the particle size of PUD and on the viscosity were investigated. As the molecular weight of PUDs increased the particle size and viscosity is not changed.