We establish the existence of topologically stable knot in two-gap
superconductor whose topology Ο3β(S2) is fixed by the Chern-Simon index of
the electromagnetic potential. We present a helical magnetic vortex solution in
Ginzburg-Landau theory of two-gap superconductor which has a non-vanishing
condensate at the core, and identify the knot as a twisted magnetic vortex ring
made of the helical vortex. We discuss how the knot can be constructed in the
recent two-gap MgB2β superconductor.Comment: 4 pages, 3 figure