Using laboratory hollow cathode spectra we have identified lines of the less common magnesium isotopologues of MgH, ^25^MgH and ^26^MgH, in the A^2^{Pi}-X^2^{Sigma}^+^ system. Based on the previous analysis of ^24^MgH, molecular lines have been measured and molecular constants derived for ^25^MgH and ^26^MgH. Term values and linelists, in both wavenumber and wavelength units, are presented. The A^2^{Pi}-X^2^{Sigma}^+^ system of MgH is important for measuring the magnesium isotope ratios in stars.