The　equilibrium　crystal　structure　parameters　and　the　total　energies　of　the　polymorphous　LaMO3　perovskites　(M　=　Al,　Ga)　and　their　constituent　binary　oxides　A-La2O3,　alpha-Al2O3　and　beta-Ga2O3　were　calculated　with　abinitio　method　based　on　density　function　theory　(DFT)　and　projector　augmented　wave　method　(PAW)　using　both　local　density　approximation　(LDA)　and　generalized　gradient　approximation　(GGA).　The　relative　lattice　stabilities　of　the　various　configurations　with　respect　to　the　ground　state　and　the　enthalpies　of　formation　of　the　stable　perovskites　from　the　constituent　binary　oxides　were　obtained.　The　enthalpies　of　formation　at　298.15　K　calculated　within　LDA,　-67.19　and　-49.99　kJmol(-1)　for　the　stable　configurations　of　LaAlO3　and　LaGaO3,　respectively,　agree　well　with　the　available　experimental　data,　while　the　enthalpies　calculated　within　GGA　are　much　less　negative.　It　was　the　first　time　that　recurred　the　experimental　enthalpies　of　formation　at　298.15　K　for　the　stable　configurations　of　LaAlO3　and　LaGaO3　from　a　fundamental　ab　initio　calculation.　(c)　2007　Elsevier　Ltd.　All　rights　reserved.