Several sets of the electron density profiles measured by the radio occultation experiment on board Mars Global Surveyor have been analyzed to investigate the dependence of the peak electron density of the Martian ionosphere on the solar zenith angle (SZA), neutral gas scale height (Hn), and E10.7, which was used as a proxy of the solar EUV radiation. Corrections have been made for the E10.7 index at the Earth orbit to obtain the E10.7 index at the Mars orbit (denoted as E*10.7). The relationship between the peak electron density (npeak)(in northern hemisphere) of the Martian ionosphere and the E*10.7, SZA and Hn is that $varepsilon$ = ln($langle$npeak$rangle$)/ln<$langle$(E*10.7 ¿ cos χ)/Hn(peak)0.33$rangle$> ≈ 0.44, slightly departing from 0.5, the value for an ideal Chapman layer. For the data set measured in the strong crustal magnetic field region (southern hemisphere), $varepsilon$ is higher than that in the nonmagnetic field region (northern hemisphere), which could be caused by the higher electron temperature in the strong magnetic field.