Abstract: A continuous process for producing O,O-di-lower alkylchlorothiophosphate very important as an intermediate for organo-phosphate series agricultural chemicals which comprises continuously reacting phosphorus sulfochloride with a lower alcohol in the presence of caustic soda according to a multi-stage reaction form comprising from 3 to 8 stages in which the following conditions are satisfied:(1) The amounts of caustic soda and a lower alcohol used shall be from 2 to 2.2 moles and 10 moles or more, respectively, based on 1 mole of phosphorus sulfochloride.(2) Caustic soda, water and the lower alcohol shall be used as a caustic soda/water/lower alcohol solution, and besides the caustic soda concentration of the aqueous caustic soda in said solution shall be from 30.0 to 99.5 wt.%.(3) To the 1st reaction stage shall be continuously supplied the whole amount of phosphorus sulfochloride required and from 45 to 85 wt.