In the atmosphere of Mars, the effect of an ionospheric layer of meteoric origin on an HF radio wave propagation is investigated. We consider the putative magnesium ion layer which results from the ablation of sporadic meteors from a work recently published. To account for day-night variability, two electron profiles are considered in an altitude range around 80 km. First we argue that there may be some observational evidence of this magnesium layer in early Mars observations that were not noticed before. Then we study the effect of this ionospheric layer on the attenuation of HF waves. For a propagation path through the ionosphere as envisaged for HF subsurface sounding on future Mars missions, the one-way attenuation may range from up to 360 dB's at 1.8 MHz and up to 18 dB's at 9 MHz. ¿ 2001 American Geophysical Union