A series of MgxZn1-xO thin films were successfully fabricated by the sol-gel method on n-type Si (0 0 1) and quartz substrates. The structural and optical properties were studied using XRD and the transmittance spectrum. The Mg0.05Zn0.95O and Mg0.15Zn0.85 alloys with wurtzite structure show high thermal stability up to 1000degreesC. However, when x is 0.36, phase separation will occur at 800degreesC. The optical band gap of MgxZn1-xO alloys (0 less than or equal to x less than or equal to 0.36) ranges from 3.4 to 3.93 eV. (C) 2002 Elsevier Science B.V. All rights reserved.