We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal (dSph) galaxy. We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the $I_{rm c}$ band show large-amplitude (3.7 and 0.9 mag) and long-period ($326pm 15$ and $122pm 5$ days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras ($75.3^{+12.8}_{-10.9}$ and $79.8^{+11.5}_{-9.9}$ kpc, respectively), together with the radial velocities available, support memberships of the Sextans dSph ($90.0pm 10.0$ kpc). These are the first Miras found in a stellar system with a metallicity as low as ${rm [Fe/H]sim -1.9}$, than any other known system with Miras.
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