Process for the manufacture of granular monohydrated sodium perborate

A process of obtaining granular monohydrated sodium perborate endowed with resistance to abrasion, starting from the corresponding tetrahydrated perborate, characterized in that a carboxylic acid mixture consisting essentially of acetic acid, or alkali metal salt thereof, and formic acid, or alkali metal salt thereof, is added to said tetrahydrated perborate, already present in the granular state, then carrying out a dehydration of the tetrahydrated perborate until the conversion to monohydrated perborate is substantially complete, wherein, at the outlet of the dehydration zone, the moisture content is from 10 to 52 g/kg, the relative humidity is from 10 to 40%, and the temperature is from 45.degree. to 60.degree. C.