The structural and magnetic properties of the series of compounds La_0.7Sr_0.3Co_1−xMn_xO₃(x=0.1,0.5,0.75,and 0.9) have been studied using DC magnetization and neutron powder diffraction techniques. All the samples crys-tallize in the rhombohedral structure. The values of TC and the magnetic moment for x=0.1 are significantly reduced from the reported values for x=0. The results are discussed in terms of an increase in negative Co³⁺-O-Mn⁴⁺inter-actions and a reduction in Co³⁺-O-Co⁴⁺double-exchange interactions.