† These authors contribute equally.Spin current is a central theme in spintronics, and its generation is a keen issue. The spin-polarized current injection from the ferromagnet, spin battery, and spin Hall effect have been used to generate spin current, but Ohmic currents in the normal state are involved in all of these methods. On the other hand, the spin and spin current manipulation by the supercurrent in superconductors is a promising route for dissipationless spintronics. Here we show theoretically that, in two-dimensional superconductors with Rashba spin-orbit interaction, the generation of dissipationless bulk spin current by charge supercurrent becomes highly efficient, exceeding that in normal states in the dilute limit, i.e. when the chemical potential is close to the band edge, although the spin density becomes small there. This result manifests the possibility of creating new spintronic devices with long-range coherence.In spintronics, spin current plays an essential role to transfer the information associated with the spin degrees of freedom. Therefore the generation of spin current is an important issue, and several methods have been proposed and experimentally verified [1]. Various methods, such as the spin polarized current injection from the ferromagnet [2-4], spin battery [5-9], and spin Hall effect [10][11][12][13][14][15][16], have been employed to generate the spin current. It has been proposed also that the spin current second order in the electric field can be generated in noncentrosymmetric systems with spin-orbit interaction [17,18]. The spin currents mentioned above are either carried by itinerant electrons through dissipative electric currents, or by localized magnetic moments through exchange interactions. However, there can also be non-dissipative spin current in itinerant-electron systems. In this case, it is an equilibrium spin current without dissipation [19]. Although such a spin current is detectable according to Sonin [20], it does not contribute to the transport property in a set up where the spin current can flow in and out.On the other hand, superconducting spintronics is an emerging field attracting recent interest [21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Although the spin degrees of freedom are usually quenched in singlet superconductors, the triplet component can be finite in noncentrosymmetric superconductors, ferromagnet-superconductor hybrids and Josephson junctions, or odd-parity superconductors, where the spins become (partially) active. Therefore, it is an intriguing issue if one can generate a spin current in superconductors with zero or small dissipation. Actually, the spin supercurrent has been discussed in He3 related to the internal degrees of freedom [39]. Recently, Leurs et al. [40] have reexamined the spin supercurrent in spin-orbit coupled systems, and classified it to the coherent and noncoherent parts, only the latter of which contributes to the continuity equation of the spin density and its gen-eration or manipulation is the focus of sup...