The preparation of spherical particles of composite alumina-chromia nature and amorphous character by a procedure of homogeneous precipitation at 100 degreesC for 1 h, from aqueous Al(III) and Cr(III) nitrate solutions containing sodium sulphate, urea and polyvinylpyrrolidone, is described. This method allows controlling the Cr/Al ratio and the mean size of the particles (in the nanometer and the micrometer range) by adjusting the reagents concentrations. The structural and compositional changes originated in the particles on calcination were evaluated. It was found that for alumina-rich compositions (Cr/Al mole ratio less than or equal to0.13), the particles transformed into fully developed corundum solid solutions at much lower temperature (1000 degreesC) than those needed for samples prepared by previously reported procedures (greater than or equal to 1300 degreesC), which was attributed to the high degree of chemical homogeneity at the atomic level attained in our case. It was also observed that an increase in the Cr/Al mole ratio of the composite systems resulted in an increase of the heating temperature required for the full development of the corundum solid solution.