  We establish the existence of topologically stable knot in two-gap
superconductor whose topology $\pi_3(S^2)$ 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 $\rm MgB_2$ superconductor.
