The effects of different molecular beam epitaxy (MBE) growth conditions on material qualities of In0.52Al0.48As on InP were investigated. Investigated parameters were growth temperature and As overpressure. A range of these two parameters within which InAlAs grows under the As-rich condition was first determined by reflection high-energy electron diffraction. Five different InAlAs samples were grown within this range and characterized by double crystal x-rav diffraction, Hall measurement, and photoluminescence. Based on the results of these characterizations, the optimal MBE growth condition for InAlAs was determined.