The grain-boundary character distribution (GBCD) of undoped MgO has been measured and compared with samples containing small concentrations of Ca, Sr, Ba, and Y. Auger electron spectroscopy measurements of intergranular fracture surfaces verified that Ca, Ba, and Y segregated anisotropically to grain boundaries (GBs). The segregation of Sr was not detected. The GBCDs of Ca, Ba, and Y doped MgO have more GBs comprised of {100} planes than the undoped material and the fractional area of these planes was highest in the Ca-containing samples. Sr impurities, on the other hand, have no measurable influence on the GBCD. The results demonstrate that GB plane distributions can be controlled through impurity additions.