The solid solubility of the SrAl2O4-CaAl2O4 system has been investigated using high resolution synchrotron powder diffraction methods. Analysis of the patterns shows there is a limited composition range at which single phase samples can be obtained, x < 0.25 and x > 0.75 for the series Ca1-xSrxAl2O4. At intermediate compositions up to three phases are observed, two monoclinic and one hexagonal. The temperature dependence of the structures is also described. Crown Copyright (C) 2002 Published by Elsevier Science Ltd. All rights reserved.