Solid-state synthesis and investigation of crystal structure and magnetic properties of Bi_0.86La_0.14−x Sm _x FeO₃ (0 ⩽ x ⩽ 0.14) ceramics were performed. It was found that a rhombohedral to orthorhombic phase transition took place in the series with decreasing average ionic radius of the substituting elements occupying the A-site of the ABO₃ perovskite. Magnetic properties of the compounds were shown to correlate with evolution of their structural state. Pure rhombohedral samples 0 ⩽ x ⩽ 0.06 were obtained in a mixed antiferromagnetic/weak ferromagnetic state. A small residual magnetization characteristic of the compounds was found to weakly depend on change of the chemical composition. Progressive increase of the residual magnetization was observed upon the rhombohedral-to-orthorhombic transition. Reasons for the appearance of the weak ferromagnetism in orthorhombic and rhombohedral phases of the Bi_0.86(La, Sm)_0.14FeO₃ compounds were analysed.