X-ray diffraction, differential scanning calorimetry, and magnetization measurements of the Bi0.825Nd0.175Fe1−yMnyO3 (y ≤ 0.3) compounds were carried out to follow the effect of Mn doping on the crystal structure and magnetic properties of the intermediate antiferroelectric and weak ferromagnetic phase of the Bi1−xNdxFeO3 perovskites. Suppression of the antipolar displacements typical of the parent B-site undoped compound followed by stabilization of the GdFeO3-type structure as well as decrease of the antipolar-to-nonpolar transition temperature were found in this series with increasing Mn content. Compositional variation of the spontaneous magnetization in the Bi0.825Nd0.175Fe1−yMnyO3 (y ≤ 0.3) system was shown to have a temperature-dependent character. At room temperature, a close to linear decrease of the spontaneous magnetization takes place with increase of the Mn content. At low temperatures, enhancement of the magnetization is observed with increasing the dopant concentration.