In this work, a thermobarometric study of bulk KNO3 submitted to pressure less than 150 MPa has been performed by means of the Metabolemeter system. The effect of pressure on the transitions between the different phases I, II and III have been analysed. Endothermic transformation from II to I takes place through phase III. On cooling from phase I, a coexistence between the phases II and III, metastable at room temperature, is always obtained.