A new diferrous complex with asymmetric coordination sites, [Fe2(μ-OBz)(L)](ClO4)2 (1) (L = N,N-bis(6-methyl-2-pyridylmethyl)-N’,N’-bis(6-pivalamido-2-pyridylmethyl)-1,3-diaminopropan- 2-ol), was synthesized, which was immobilized in the internal surface of mesoporous silica (FSM-16) to construct a functional material (1A). The reaction of 1 with O2 in acetone at –50°C generated a peroxo complex 2 [λmax = 589 nm (ε = 2200 M-1 cm-1), ν16O-16O = 890 and 908 cm-1 (ν18O-18O = 852 cm-1)]. The μ-peroxo complex 2 was decomposed by bubbling of Ar gas without releasing O2, but the reaction of 1A with O2 at ambient temperature also formed a peroxo complex (2A) without decomposition. The reflectance spectrum of 2A showed a band assignable to the LMCT band from peroxo to a Fe(III) ion at 588 nm. Compound 2A is very stable, whose half-life time is 45 min, in contrast to a short life of 2 (310 sec). 2A released dioxygen by heating up to 75°C in vacuo, which was regenerated by bubbling of dioxygen at ambient temperature.