Structural analysis of branched DNA molecules (BDM) is important as model systems for DNA junctions and also as building units for DNA assembly. Although there have been efforts to study the structures of BDM, label-free solution structures have not been well determined yet. Here, we used a combination of synchrotron-based experimental tools and computational simulation to study the global structures of label-free BDM in solution. Overall structures of 3-arm and 4-arm BDM were revealed as an asymmetric T(or Y)-shape and a distorted X-shape, respectively. The internal structures of the DNA double helix were shown to have a canonical B-form for both the BDM. We also reconstructed the thermal denaturation process of BDM by determining the transient global structures over a wide range of temperatures. The proposed high-resolution structures of BDM are expected to provide fundamental information for studies of the biological function of junction DNAs and DNA assembly.