Acicular crystals were grown in gallium oxynitride powder prepared by ammonia nitridation of amorphous gallium oxide precursors containing less than 5 at% of either Ni or Co, via the citrate route. The crystals were several tens of nanometres wide, several micrometres long, and grown in the temperature range 750 to 850 °C in a flow of ammonia of less than 200 mL min −1 . The crystal structure of the gallium oxynitride was a highly disordered 2H wurtzite-type with some 3C zinc blende-type stacking faults. The crystals grew in their basal plane changing their aspect ratio with the supplying method of small amounts of Ni or Co and an amount of residual carbon. The acicular crystals were grown by the catalytic behavior of Ni or Co to enhance one-dimensional growth in the hexagonal c -plane. Gallium oxynitride nanofibers were grown one-dimensionally in the c -plane of the wurzite-type lattice via a non-VLS mechanism with nickel or cobalt impurity.