Sintering aids or dopants have often been used successfully to limit the grain growth of alumina during sintering. Recently codoping of alumina with transition elements has been reported to produce additional effects in comparison to single doping in enhancement of creep and real in-line transmittance of light. The current study attempts to address the issue of the atomistic mechanism behind these experimentally observed codoping effects. The effect of codoping on the atomistic structure of a series of La–Y, Mg–Y, La–Mg codoped -alumina interfaces was studied using energy minimization calculations. The segregation energy for single doping as well as codoping is negative for all the surfaces and grain boundaries. While, there is no significant energetic gain for La–Y cosegregation in comparison to single doping whereas segregation energies for Mg–Y and Mg–La codoping is more negative than single doping. A specific arrangement of dopants (associative effect) is also observed in La–Y codoped interfaces. Both mechanisms can thus contribute to the improved microstructures and properties.