Nanocrystalline La 0 . 7 Sr 0 . 3 MnO 3 (LSMO) has been synthesized by an alkali metal nitrate flux process at a relatively low temperature of 600 o C. Scanning electron and transmission electron microscopic images show that LSMO grains are of good crystallization and uniform size distribution. Inductively coupled plasma and elemental analyses indicate that the content of K + is no more than 0.6% in all the samples and the stoichiometry of La, Sr and Mn is very close to the expected value. A significant enhanced magnetoresistance is observed in the nanosized LSMO especially at low temperatures. By improving grain crystallization, the surface spin-glass behavior disappears, and the blocking temperature corresponding to the super-paramagnetic transformation shifts to a higher temperature.