In a method for preparing cerium carbonate powder by mixing a cerium precursor solution with a urea solution and carrying out a precipitation reaction, wherein the cerium carbonate powder has a hexagonal crystal structure, by using at least one type of organic solvent as a solvent for either or both the cerium precursor solution and the urea solution, and adjusting temperature of the precipitation reaction within a range of 120° C. to 300° C. Also, the method can yield cerium carbonate powder, cerium oxide powder from the cerium carbonate powder, and CMP slurry including the cerium oxide powder as an abrasive. In the method, urea as a precipitant can improve the uniformity of a reaction, and thus it is possible to easily and inexpensively obtain cerium carbonate powder with a hexagonal crystal structure without the danger by high-temperature high-pressure and the need for an expensive system in hydrothermal synthesis.