Reaction injection molding (RIM) process conditions for polydicyclopentadiene (PolyDCPD) were optimized by using a Box-Behnken design (BBD) from the response surface methodology (RSM). The RIM process parameters, such as smoke time, exotherm time, highest exotherm and PolyDCPD conversion, were tuned by changing the variables (the amount of catalyst, cocatalyst and moderator). Under the optimized condition, the ring-opening metathesis polymerization reaction of dicyclopentadiene did not occur within 100 s, the maximum temperature was reached within 4 min, and the polydicyclopentadiene conversion was over 98%. Therefore, dicyclopentadiene could be safely put into the mold in a total cycle time of less than 6 min and produce PolyDCPD with mechanical properties sufficient for industry applications.