[en] Full text: Studies on cerium-based nanostructured materials indicate that rare earth minerals can be used as catalysts for several chemical processes. Brazil is one of the countries with significant reserves of rare earth minerals, such as monazite and allanite, which have cerium as constituent. The main purpose of this research is to produce polycrystalline perovskite-type BaCeO_3-δ powder using oxalate co-precipitation method, and to evaluate the influence of synthesis methods on phase formation. The methodology consists on the precipitation of oxalates containing barium and cerium atoms. Precipitation pH was fixed at 10 and is achieved by the addition of triethylamine. The precipitate is filtered, washed and dried. The final powder is produced by heat treatment of the precipitate at 950 deg C for 5 hours. Powders were characterized by XRD and SEM. The formation of orthorhombic perovskite phase of BaCeO_3-δ was detected, and the Williamson-Hall equation was used to measure the average crystallite size in nanoscale. There was, however, a formation of small amounts of secondary phases. One the major advantages of the methodology used is the product's uniform morphology and high thermal stability of nanoparticles, thus indicating BaCeO_3-δ catalysts can used be efficiently under high temperatures. (author)