Abstract: The experiments which we carried out will inform us about the conditions of a better decomposition of phosphate of Djebel Onk (Algeria). The purpose of this study is to compare the convertion rates of the P2O5 of rock phosphate obtained by nitric attack and sulphuric attack. The reactions are carried out by varying the reaction time from 3-90 min, the temperature from 20-90°C and the granulometry of phosphate of 500-40 �m. A series of rock phosphate samples was attacked by the 2 acids and the P2O5 was dosed by gravimetry. We noted that the reaction is very fast since at the end of 3 min only, we obtained a convertion rate of P2O5 higher than 60%. A maximum convertion rate of 96.54% was obtained by the sulphuric attack in the following conditions: Temperature = 50°C, Reaction time = 60 min, Granulometry of phosphate = 50 �m. The convertion rate starts to decrease at a temperature higher than 60°C for the nitric attack and at a temperature higher than 50°C for the sulphuric attack. We also deduced that a phosphate granulometry ranging between 80 and 40 �m gives a better dissolution.