Nano——rod calcite was discovered in a loess——paleosol sequence with the TEM investigation for the sam plesfrom the Luochuan section． The diameter of the calcite is 30～ 50 nanometer and the length from hundredsnanometer to several micrometer． Nano—rod calcite crystals are round fibers with varying thicknesses． Thecrystals are bended along the direction of the crystal length．They sometimes have interlaced arrangement，andarborescent Or frame form s． The EDS reveals small am ounts of magnesium ， phosphorous and sulfur．M orphology and composition analysis indicate that the formation of the nano—rod calcite is involved in matterderived from m icroorganisms and mineralization．The forming condition of the nano— rod calcite should be anindicator of paleoclimate，paleoenvironment and paleoecology．Therefore，the discovery of nano—rod calcite inthe loess—paleosol sequence provides a new clue for reconstructing the paleoclimate and is of significance in theresearch of nanom eter m inerals in environment，genesis of carbonate in loess and paleoclimate reconstruction．