Low-temperature magnetotransport and magnetization measurements have been performed at high magnetic fields in samples of a layered artificial ferrimagnet: multilayers made by sequential sputtering of Gd and Co. Strong interfacial reaction leads to severe alloying and, if the Co layer is nominally thick enough (≳4 nm), the samples are mainly comprised of alternated pure Co and Gd0.7Co0.3 alloy layers. Such spin systems are antiferromagnetically coupled at the interface region, and the compensation temperature of this “giant” ferrimagnet is determined by the thickness of Gd and Co layers. Both magnetization and magnetoresistance measurements indicate the so-called spin-flop transition at temperatures below the Curie point of the alloy layer (∼180 K). Spin-flop magnetoresistance resembles the anisotropic magnetoresistance of ferromagnets except for the field range in which it develops: H>103–104 Oe for modulation length of ∼15 nm. The effect arises in the Co layers from anisotropic carrier scattering.