In this work, synthesis of nanocrystalline (CoCoxAl2-xO4)-Co-II-Al-III (where x=0, 0.5, 0.8, 1, 1.18 and 2) spinels by the thermal decomposition of complex precursors derived from metal nitrate salts and ethylenediaminetetraacetic acid (EDTA) has been systematically studied. Based on XRD, FTIR, DTA, TGA, SEM and TEM analyses, it has been found that the as-prepared metal organic precursors with different Co and Al contents display different thermal behavior, crystal development and particle morphology. Increment of Co content in precursors improves the degree of crystallinity of the powder. Treated at 400degreesC, in contrast to the well formed Co3O4 or Co3O4-like spinel structure for the powder precursors containing higher Co content, most of the powders from precursors containing lower Co content are still amorphous. Higher Co content in the precursors slightly decreases the unit cell parameters of the resulting (CoCoxAl2-xO4)-Co-II-Al-III spinels. Prepared at 900degreesC, the unit cell parameters of (CoAl2O4)-Al-II, (CoCo0.5Al1.5O4)-Co-II-Al-III, (CoCoAlO4)-Co-II-Al-III, (CoCo2O4)-Co-II-O-III are 8.1038, 8.1007, 8.0867, and 8.0834 Angstrom respectively. Based on this work, preparation of a series of the (CoCoxAl2-xO4)-Co-II-Al-III spinels including black or bright blue (CoAl2O4)-Al-II, (CoCo0.5Al1.5O4)-Co-II-Al-III, (CoCoAlO4)-Co-II-Al-III, (CoCo2O4)-Co-II-O-III from EDTA-Co(Al) complexing precursor has been established. (C) 2004 Kluwer Academic Publishers.