In order to decrease the firing energy of B/KNO₃ composition ignited by the exploding foil igniter, the components of B/KNO₃ were refined, and the loading density was optimized. The firing experiments were carried out using Bruceton method with the loading density of 1.50-1.64 g?cm-³, and the fire capacitance of 0.12 μF. The burst current of ultrafine B/KNO₃ composition ignited by the exploding foil igniter was also tested. Results show that the average value of 50% firing energy of ultrafine B/KNO₃ composition ignited by the exploding foil igniter is 29 mJ, and the all-fire burst current is about 500 A.