Abstract: The concentration of Phase II sodium tripolyphosphate in the sodium tripolyphosphate produced by spray drying a feed liquor comprising sodium orthophosphate, sodium pyrophosphate or mixture thereof, is increased to at least 90% by weight of sodium tripolyphosphate product, by seeding the feed liquor with Phase II material. Phase II yield is further increased by introducing with the feed liquor, in addition to the Phase II seed material, a minor amount of sodium sulfate. Hydrolysis of the Phase II seed is minimized by concentrating the Phase II seed in feed liquor in a separate feed tank at a lower temperature than the main feed line. Dispersing the Phase II seed in water, a dilute soda ash solution or an inert organic liquid and then injecting the dispersion into the feed liquor into the spray dryer promotes good contact between the seed and feed.