Recent studies concerning structure of cross-linked rubber verified experimentally and theoretically are summarized, where is shown that the real structure is different significantly from a molecular cross-linked model known conventionally. (1) Cross-linked rubber consists of heterogeneous structure of cross-linked phase and uncross-linked phase where both the phases are separated making co-continuous structure. Volume fraction in the system is 65~70% for the cross-linked phase and 30~35% for the uncross-linked phase. (2) The cross-linked phase is crosslinked tightly in a molecular scale, then it hardly deforms at an external deformation. In contrast, the uncross-linked phase seems not to be crosslinked keeping the original uncross-linked and liquid state, thus it mainly deforms under the external deformation and absorbs most solvents in a swelling test. (3) AFM image describes the crosslinked structure of rubber almost correctly, where the phase-separated structure is shown clearly as indicated by the simulation.