Magnetic and electronic states in (LaMnO3)(2)(SrMnO3)(2) superlattices fabricated on an (LaAlO3)(0.3)(SrAl0.5Ta0.5O3)(0.7) substrate, which exhibit a large nontrivial negative magnetoresistance (MR) effect, have been investigated. The crystal structure and the Mn valence state were determined using x-ray scattering measurements near the Mn K edge. These measurements revealed that the Mn valences in the LaMnO3 and SrMnO3 layers are 3+ and 4+, respectively; that is, valence modulation coincides with the La/Sr stacking structure. The Mn spin structure was studied by means of resonant soft x-ray scattering at the Mn L-2,L-3 edge and neutron magnetic scattering measurements. We succeeded in detecting a magnetic signal indicating ferromagnetism at the interface. Finally, we suggest that the origin of the MR is the competition between ferromagnetism at the interface and underlying antiferromagnetism.