The internal magnetic field (H-n) at Fe-57 nucleus was investigated for the mixed crystals NBu4[Mn(II)Fe(III)(x)Cr(III)(1-x)(ox)(3)] (x = 0 04 - 1.0) by using Mossbauer spectroscopy, where NBu4+ = tetra(n-butyl)arnmoniuln ion and ox(2-) = oxalate ion. The angle (Theta) between H-n and the principal axis of V-ZZ was observed to change from similar to 50 degrees to similar to 10 degrees with the decrease of the x value (V-ZZ = the principal component of the electric field gradient tensor); the plot of Theta against x indicates 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 ox(2-) ligands. The Theta values estimated for the Fe-57 nuclei in the bivalent and tervalent sites of NBu4[Fe(H)(0.03)Mn(II)(0.97)Fe(III)(0.02) Cr(III)(0.98)(ox)(3)] were similar to each other.