NOVELTY - A nonaqueous electrolyte secondary battery has a positive electrode (4) containing positive electrode active material particles, and a negative electrode (6). Each positive electrode active material particles have a central portion formed of olivine-type lithium iron phosphate, an intermediate portion containing lithium iron phosphate (A), and a surface portion arranged around intermediate portion and containing a lithium iron phosphate (B). The molar concentration ratio of phosphorus to iron in lithium iron phosphate in the central portion is larger than that of phosphate (A).    USE - Nonaqueous electrolyte secondary battery. Uses include but are not limited to power supply for hybrid vehicles, mobile telephone, notebook personal computer, etc.    ADVANTAGE - The positive electrode active material of nonaqueous electrolyte secondary battery has excellent water resistance and light diffusion property.    DETAILED DESCRIPTION - A nonaqueous electrolyte secondary battery has a positive electrode containing positive electrode active material particles, and a negative electrode containing lithium titanate. Each positive electrode active material particles have a central portion formed of an olivine-type lithium iron phosphate (LiFePO4), an intermediate portion arranged around the central portion and containing a lithium iron phosphate of formula: LiFexPyOz (A), and a surface portion arranged around the intermediate portion and containing a lithium iron phosphate of formula: LiFeaPbOc (B). The molar concentration ratio of phosphorus to iron in the lithium iron phosphate in the central portion is larger than the average of x/y of the phosphate (A). The average of a/b of phosphate (B) in the surface portion is smaller than the average of x/y of the phosphate (A) in the positive electrode active material particles. The central portion has a region (R) in which the x/y of the phosphate (A) continuously or intermittently increases from the surface portion side towards the central portion side.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of nonaqueous electrolyte secondary battery.    Cylindrical container (1)    Insulator (2)    Electrode group (3)    Positive electrode (4)    Negative electrode (6)