Bismuth-doped tin dioxide nanosized particles (nano-BTO)/waterborne polyurethane (PU) composite coatings were prepared by the in-situ polymerization method.The influences of nano-BTO on the reaction kinetics of synthesizing polyurethane were studied.The results showed that reaction rate between the —NCO and —OH groups increased when nano-BTO was added.nano-BTO was highly active and the Sn atom acted as the catalyst which reduced the activation energy between the —NCO group and —OH groups from 18.71 kJ·mol-1·K-1 to 16.29 kJ·mol-1·K-1.