The internal magnetic field (Hn) at57Fe nucleus was investigated for the mixed crystals NBu4[Mn(II)Fe(III)xCr(III)1−x(ox)3] (x = 0.04–1.0) by using Mössbauer spectroscopy, where NBu4+= tetra(n-butyl)ammonium ion and ox2−= oxalate ion. The angle (Θ) betweenHnand the principal axis ofVZZwas observed to change from ∼50∼ to ∼10∼ with the decrease of thexvalue (VZZ= the principal component of the electric field gradient tensor): the plot of Θ againstxindicates that the Cr(III) spins in NBu4[Mn(II)Cr(III)(ox)3] are aligned along an axis almost perpendicular to the honeycomb layers consisting of an alternate array of Mn(II) and Cr(III) ions through ox2−ligands. The Θ values estimated for the57Fe nuclei in the bivalent and tervalent sites of NBu4[Fe(II)0.03Mn(II)0.97Fe(III)0.02Cr(III)0.98(ox)3] were similar to each other.