In this communication, the effects of testing conditions, i.e., reaction time and temperature, on the accuracy for determining epoxy index of chloroepoxy propane were investigated, in order to reduce errors generated by using the current Chinese Standard GB1677-81 for determining epoxy indexes of epoxy resins. Experimental results showed that, for chloroepoxy propane reacting with hydrochloric acid-acetone for 4 h at 45°C, its epoxy index was very close to the theoretical value. The relative error of this improved method was ca. 0.40%, much lower than that determined by the method defined in GB1677-81, which results in the maximum error of 6.77%.