The present invention relates to a process for the manufacture of disodium phosphate of a high purity without utilizing organic solvents. According to the process, monosodium sulfate is reacted, at a temperature, in the range of 40 to 100 degrees C. with a phosphate constituent selected from phosphate rock, dicalcium phosphate or mixtures thereof, in the presence of phosphoric acid. The common metal impurities, organic matter and fluorides present in the starting phosphate rock are substantially complete eliminated with the solid gypsum or dicalcium phosphate resulted thereto. After separating said solid, the filtrate is treated in two neutralization stages: first by a calcium constituent selected from calcium carbonate, calcium hydroxide or mixtures thereof and separating the formed dicalcium phosphate, followed by a second neutralization with an alkali sodium constituent selected from sodium hydroxide, sodium carbonate and sodium bicarbonate or mixtures thereof at a pH in the range of 8.0 to 9.5. From the resulted filtrate, pure disodium phosphate is obtained by crystallization. The process is characterized by a high recovering of the P.sub.2 O.sub.5 and Na.sub.2 O values, the resulted product being substantially free of chloride ion.