About 0.4-mu m-thick GaN films were epitaxially grown on a LaAlO3(100) substrate by rf plasma assisted molecular beam epitaxy. The growth mode was monitored by reflection high-energy electron diffraction and the crystalline quality of the GaN films was characterized by X-ray diffraction and transmission electron microscopy. The matching face relationship between GaN and the LaAlO3(100) substrate was [0001]GaN parallel to [100]LaAlO3 and [01 (1) over bar 0]GaN // [0 (1) over bar 1]LaAlO3, and a lattice mismatch of similar to 3% for the [0 (1) over bar 1] plane was estimated.