Fe-24Cr-12Co-1.5Si ribbons were prepared by simple melt spinning and aging processes, and their microstructure and phase transition were studied. The average grain size of the aged ribbons is ∼4.22 μm, much smaller than that of traditional bulk Fe-Cr-Co alloy. The as-spun ribbons are mainly composed of BCC-type α and FCC-type Cr(M). During aging treatment, the Cr(M) phase firstly partly transforms into (CrSi)0.99(FeCo)1.01 at the initially higher aging temperature, accompanied by the continuous spinodal decomposition of α→α1+α2, and at the lower aging temperature the residual Cr(M) and α turn into Fe(Si,M)2 (M = Cr, Co) and Co2Si rather than (CrSi)0.99(FeCo)1.01. And a new uniform cellular microstructure is formed in the ribbons after multi-stage aging, in which the (Fe,Co)-rich α1 phase is located in the cellular interior, while the Cr-rich α2 phase concentrates in the cellular boundaries.