About 0.4 mu m thick GaN films were epitaxially grown on a LaAlO3(1 0 0) substrate by RF plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction (RHEED) observation showed that the growth mode changed from island to lateral growth. The crystalline quality of the GaN film was characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The epitaxial relationship between GaN and the LaAlO3(100) substrate was [0001]GaN//[100]LaAlO3, [01 (1) over bar 0]GaN//[0 (1) over bar 1]LaAlO3, and [2 (1) over bar (1) over bar 0]GaN//[011]LaAlO3. A lattice mismatch of similar to 3% for the [0 (1) over bar 1] plane was estimated. The GaN film exhibited a near band-edge peak of 3.463 eV by photoluminescence (PL) measurement at room temperature.