The present paper presents a process of purification of residual waters coming from the manufacture of acrylonitrile with recovery of cyanhydrines. This process consists in separating cyanhydrines in a watery concentrate through superheat-expansion-condensation and alkaline split, respectively, in sodium cyanide and in carbonylic constituent. Carbonylic constituent is successively separated by steamed dragging in order to avoid some methods of minor importance.