  Recent theoretical studies suggest the existence of low-mass zero-metal stars
in the current universe. In order to study the basic properties of the
atmosphere of low-mass first stars, we performed one dimensional
magnetohydrodynamical simulations for the heating of coronal loops on low-mass
stars with various metallicities. While the simulated loops are heated up to
>$10^6$ K by the dissipation of Alfvenic waves originating from the convective
motion irrespectively of the metallicity, the coronal properties sensitively
depend on the metallicity. Lower-metal stars create hotter and denser coronae
because the radiative cooling is suppressed. The zero-metal star gives more
than ten times higher coronal density than the solar-metallicity counterpart,
and as a result, the UV and X-ray fluxes from the loop are (1-5) times higher
than those of the solar metallicity star. We also discuss the dependence of the
coronal properties on the length of the simulated coronal loops
