To monitor and systematically control viscous behaviors of polyurethane (PU) prepolymer in the preparation of PU dispersion (PUD), 80L scale pilot reactor to which programmable logic control (PLC) was installed capable of operating each of process instruments, automatically using personal computer (PC) was built. In this pilot reactor, PU prepolymer was synthesized with polycarbonate diol (PCD), dimethylol propionic acid (DMPA), and isophorone diisocyanate (IPDI). The effect of temperature conditions, mixing efficiency, and recipe change on the viscous behaviors, molecular weight, and re-productivity of various property of PUD was in detail investigated.