The electronic transport property and band structure of pure gallium nitride, oxygen,°uorine, indium substituted gallium nitride nanoribbon and defect structured GaN nanoribbons are investigated by employing¯rst-principles studies using density functional theory. The band structure of pure GaN and indium substituted GaN nanoribbon shows a semiconducting nature. The oxygen,°uorine substituted GaN and defect structured GaN results in metallic behavior. The density of states provides the insight for the localization of charges in the valence band and conduction band. The substitution of oxygen and°uorine enhance the density of charges in valence band and conduction band. The substitution of indium shows an increase in the peak amplitude in density of states. The presence of defect also increases the density of states. The transport properties are studied in terms of transmission spectrum; pure GaN and indium substituted shows a same trend in transmission. In contrast, the transmission can be enhanced by the substitution of oxygen,°uorine and defect in nanoribbon. The information provided in the present study will pave its way to tailor a new material of GaN nanostructures with improved performance in the optoelectronic devices.