A direct method to synthesize porous hausmannite (Mn3O4) microparticles by the KMnO4-AC reaction and combustion system is reported in this paper. In order to synthesize the manganese oxide, four experimental factors were considered: pH (3.0, 4.5 and 6.0), AC content (2.08 x 10(-2) and 8.33 x 10(-2)M), initial Mn(VII) content (4.55 x 10(-4) and 9.1 x 10(-4) M) and stirring velocity (300 and 500 rpm). The AC was added to the Mn(VII) aqueous solution and stirred for 2 h. For different pH levels, the Mn(VII) content in the solution was measured by UV/Vis spectrometry at 540 nm in order to evaluate the Mn reduction. Later, the manganese-loaded AC was calcined at 700 degrees C in dry air at 1900 sccm during 60 min, indicating that the Mn3O4 content is directly proportional to the acidity of the solution. Spongy and porous Mn3O4 microparticles were synthesized considering the following levels: pH (3.0), an AC content (8.33 x 10(-2) M) and an initial Mn(VII) content (9.1 x 10(-4) M) with 500 rpm.