The structural and optical properties of GaN nanowires (NWs) grown by catalytic and self-catalytic-assisted vapor liquid solid approach using chemical vapor deposition (CVD) are reported. Liquid gallium droplets were used as the nucleation centre for the growth of self-catalyst assisted NWs, whereas pre-deposited Ni and Au thin films were employed as the seed layer for the catalyst-assisted growth on Si (111) substrates. Electron microscopy analyses revealed that the growth rates and densities of the structural defects of the NWs strongly vary with the nature of the catalyst. The high resolution electron microscopy and selected area electron diffraction studies exhibit a high crystalline quality of Ni-catalyst-assisted GaN NWs, whereas self-catalytic NWs contain defects such as stacking faults and cubic inclusion. Temperature-dependent photoluminescence on the ensembles of NWs illustrates the absence of the characteristic yellow luminescence band of GaN for the Ni-assisted vapor-liquid-solid approach, implying the high optical quality of GaN NWs by CVD. The results show that the quality of the self-catalytic GaN NWs grown by CVD is yet to be improved for device applications. This journal is © the Partner Organisations 2014.