To present a nonaqueous electrolyte secondary battery using iron compound which is inexpensive and abundant in resource, as the active material for the positive electrode. An iron compound with particle size of 1 to 300 nm or less, being composed of substantially spherical primary particles of pore-free matter, is used as the active material for a positive electrode, which is used together with a negative electrode and a nonaqueous electrolyte for composing the battery. By forming the primary particles for composing particles of the iron compound as a pore-free matter, being controlled in a range of 1 to 300 nm, nano effects are brought about, and it is also effective to suppress excessive increase of surface area which may lead to promotion of decomposition of electrolyte, and an excellent discharge capacity is realized stably for a long period.