Pseudo-cubic LaMnO3+delta powders were obtained by pyrolysis of the amorphous residue of the hydrothermal treatment, at 150degreesC under autogeneous pressure, of lanthanum and manganese nitrates in presence of citric acid. The pyrolysis steps are identified by coupled T.G.A.-D.T.A. determining also the carbon content evolution. From F. T. I. R. and W. A. X. S. investigation of the amorphous powders calcined at various temperatures in the 200 - 1000degreesC range, it is shown that the crystallization occurs slowly in the 550 - 700 degreesC range and that the perovskite skeleton already exists in the amorphous citrate precursors formed by the hydrothermal treatment. (C) 2004 Kluwer Academic Publishers.