The saturable absorption properties of Co^2  +  :  MgAl₂O₄ crystals in three different cutting directions were studied experimentally. The characteristic of the transmission of polarized incidence light through the [100], [110], and [111]-cut Co^2  +  :  MgAl₂O₄ single crystal was investigated. The [110]-cut crystal had the maximum transmittance observed. We conclude that using a [110]-cut Co^2  +  :  MgAl₂O₄ crystal to form a Co^2  +  :  MgAl₂O₄  /  Er,Yb:glass passive Q-switched microchip laser can improve the output characteristics of the laser, such as pulse energy and extinction ratio without changing any other parameters.