There is provided a process capable of preventing the adhesion of a catalyst to an evaporator in a step of separating a chlorophosphite as a target substance from a reaction liquid by evaporation. The process includes a first step of allowing phosphorus trichloride and a phosphorous acid triester represented by (RO)3P to react in the presence of a catalyst having a viscosity at 80° C. of 100 mPa·s or lower to produce a chlorophosphite represented by RO(R′)PCl, and a second step of vaporizing a reaction liquid containing the chlorophosphite obtained in the first step, in a short time, to separate the catalyst.