Manganese oxidic mesoporous particles of nominal size in the micrometer region have been prepared by controlled hydrolysis of the trinuclear complex [Mn3O(CH3COO)(6)(pyr)(3)]ClO4(pyr:pyridine). The cation of the complex, which is unstable in water, was hydrolized in various baths containing additives like M(CH3COO)(2) (M=Mn, Ni), M'(NO3)(2-3) (M'= Ni, Mn, La, Co, Fe), LiOH, and CH3COOH. The resulting dried products of hydrolysis possess surface areas as high as 200-400 m(2)g(-1) at T less than or equal to 300 degrees C, 50-200 m(2)g(-1) around 400 degrees C, and 20-100 m(2)g(-1) at T = 500-600 degrees C depending on the additive. The particle thus obtained shows no hysteresis loop in the adsorption-desorption of N-2 at 77 K. The alpha(s) plots indicate that the obtained solids are mesoporous, The calculated pores are in the range of 5-10 nm, corresponding most probably to interparticle void space. Particle size analysis showed that the formed particles are in the micrometer region and SEM photographs reveal micrometer scale particles, too. Plots of lnV(ads) vs ln[ln(P0/P)], where V-ads is the volume of N-2 adsorbed at T = 77 K and relative pressure P/P-0, reveal a surface dimentionality D of the particles equal to 2.56 +/- 0.05. This value approaches the fractal dimentionality of the Koch pyramid 2.58497, and a model is proposed for building up such Koch-like porous particles from Mn4O or MnO4 tetrahedra.