Monodispersed particles of doped yttrium basic carbonates were prepared at aging at elevated temperature corresponding salts solutions in the presence of urea. Coprecipitation in mixed solutions of yttrium, lanthanum and neodymium salts under similar experimental conditions yielded composite particles of basic carbonates. The content of the three metals in the solids followed closely the initial composition of the reacting solutions. On calcination all prepared solids converted to their corresponding oxides while retaining their particle morphology. The so-prepared powders were characterized by various techniques. Monodispersed particles of doped yttrium basic carbonates were prepared at aging at elevated temperature corresponding salts solutions in the presence of urea. Coprecipitation in mixed solutions of yttrium, lanthanum and neodymium salts under similar experimental conditions yielded composite particles of basic carbonates. The content of the three metals in the solids followed closely the initial composition of the reacting solutions. On calcination all prepared solids converted to their corresponding oxides while retaining their particle morphology. The so-prepared powders were characterized by various techniques.