We report on the synthesis of Mn3O4 nanoparticles via a two-step hydrothermal route by using Mn(CH3COO)(2) as the only starting material and TMAOH and NaOH as hydrolysing agents. XRD and FT-IR analyses confirmed the composition and structure of Mn3O4. TEM images showed that spheroid Mn3O4 nanostructures obtained by this method have average particle size of 6 and 14 nm for NaOH and TMAOH hydrolyzed samples respectively. Particle size analysis indicated a strong aggregation of nanoparticles and exhibited bi-modal distribution with average size of aggregates as similar to 250 nm and 1.1 mu m for both samples. Zeta potential analysis revealed adsorbed TMAOH species on the surface of Mn3O4 nanoparticles hydrolyzed using TMAOH. ESR analyses resulted in broader lines and smaller g values than bulk Mn3O4 nanoparticles, probably due to the exchange-coupled system with unlike spins such as canted spin at surface of high-surface-disordered nanoparticles.