The crystal structure of both Bi 0.5 Sr 1.5 YCu 1.5 Fe 0.5 O 6 and Sr 2 Pb 0.5 Y 0.5 CuFeO 6 is basically composed of double layers of (Cu,Fe)O 5 pyramids. In order to better understand the magnetic properties of this type of compound, a 57 Fe Mössbauer spectroscopy study in the temperature range 4.2–380 K was undertaken. The Mössbauer spectra of both compounds studied present a strong relaxational character. The lines, magnetically split at 4.2 K, become broader and more asymmetrical with increasing temperature. The amount of the paramagneticaphase increases drastically and the magnetic splitting vanishes at 340 K for Sr 2 Pb 0.5 Y 0.5 CuFeO 6 and at 295 K for Bi 0.5 Sr 1.5 YCu 1.5 Fe 0.5 O 6 . The results are discussed in terms of the superexchange interactions between the Fe atoms placed in the basal planes of the quadratic pyramidal layers and of the FeCu superexchange. The relaxational character of the Mössbauer spectra offers evidence for a gradual freezing of the Fe spins, reminiscent of the behaviour of concentrated spin glasses.