Crystal structure of Ga2O3 nanocolumns grown on MgO substrate is analyzed by electron microscopy and electron diffraction study. The nanocolumns have beta-Ga2O3 structure and the growth direction is [0 0 1] directions. A thin gamma-Ga2O3 layer grows on the substrate to relax the lattice misfit between MgO and beta-Ga2O3. The bottom layer of the 7 form layer is disordered by {110} stacking faults. Poly crystalline structure that consists of beta-Ga2O3 and gamma-Ga2O3 nanocrystals exists between the P form nanocolumns and the gamma form layer. The gamma form changes gradually to the P form growing up to the nanocolumn. Though various crystal forms appear in a specimen, oxygen cubic close-packed lattice in crystal structures has always the same orientation in all layers including the MgO substrate. (c) 2005 Elsevier B.V. All rights reserved.