In view of the study of the chemistry of the oxalate coprecipitation process for preparing BiSrCaCuO superconductors, the characteristics of oxalates of calcium and strontium in the Ca(NO3)(2)-Sr(NO3)(2)-HNO3-H2O-(NH4)(2)C2O4 system are investigated. Based on XRD, SEM and TG a comparison between the crystal structure, morphology and thermal decomposition behavior of coprecipitated and physically mixed calcium and strontium oxalates with the same Ca/Sr stoichiometry is made. It is shown that the coprecipitated powders form homogeneous solid solutions of which the crystal structure, morphology and thermal behaviour depend on the Ca/Sr stoichiometry.