theta aEuro(3)-phase, with a formal stoichiometry of Al3Cu, is a coherent, metastable precipitate (GP-II) phase commonly found in Al-based aerospace alloys. In this paper, we employed a first-principles based method to study the energetics of the Al/theta aEuro(3) interface as response to external strains. The potential effects of temperature, Cu activity, and different strain modes on interface energy (gamma (3)(Al/theta aEuro)) were systematically investigated. Calculations show that (i) an unstrained gamma (3)(Al/theta aEuro) always increases with temperature: as temperature increases from T = 298 to 498 K, gamma (3)(Al/theta aEuro) increases by 9.0 %; (ii) gamma (3)(Al/theta aEuro) is more sensitive to compressive strains than to tensile strains of the same magnitude. In particular, for a parallel compressive strain increasing from 0 to 2 % at a typical aging temperature, gamma (3)(Al/theta aEuro) decreases by 6.6 %, while a vertical compressive strain of 2 % has a slightly stronger impact by decreasing gamma (3)(Al/theta aEuro) by 9.6 %. Different influences of applied strain/stress on the formation energies of different orientated interfaces can be further exaggerated by the Poisson effect, and eventually affect the preferential precipitation orientation of theta aEuro(3) in the matrix.