A binuclear iron(III) complex bridged by trans-1,2-bis(4-pyridyl)ethylene, [LFeIII(vibpy)(FeL)-L-III](BPh4)(2), showed a gradual two-step spin crossover behavior, where H2L is bis(3-methoxysalicylideneaminopropyl)methylamine and BPh4- is tetraphenylborate. The single-crystal X-ray analysis at the intermediate state revealed that one of the two Fe-III ions of the binuclear complex is in the high-spin (HS) state and the other is in the low-spin (LS) state. The HS and LS sites independently form layers and these HS and LS layers alternately stack.