In order to redefine the kilogram, the only SI base unit still defined by material artifact, the International Avogadro Coordination (IAC) Project was organized by the International Committee for Weights and Measures (CIPM) in 2004. Seven national metrology institutes and the International Bureau of Weights and Measures (BIPM), including the National Metrology Institute of Japan (NMIJ) of AIST, are involved in this project. We hope that the new silicon crystal made of pure ²⁸Si produced in the project will achieve fundamental reduction of uncertainty in the determination of the Avogadro constant. In May 2007, a 5 kg of ²⁸Si crystal with an enrichment factor of 99.99 % was successfully grown by the cooperation with the Russian and German institutes. After two 1 kg spheres were polished from the crystal, one of the spheres came to NMIJ in April 2008 for its density measurement. The project has entered its last phase of measurement, and final results will be available by the end of 2009.