Manipulation of the surface architecture of semiconducting nanowires with a control in surface polarity is one of the important objectives for nanowire based electronic and optoelectronic devices for commercialization. We report the growth of exceptionally high structural and optical quality nonpolar GaN nanowires with controlled and uniform surface morphology and size distribution, for large scale production. The role of O contamination (∼1 to 10 5 ppm) in the surface architecture of these nanowires is investigated with the possible mechanism involved. Nonpolar GaN nanowires grown under O rich conditions show inhomogeneous surface morphologies and sizes (50-150 nm) while nanowires have precise sizes of 40(±5) nm and uniform surface morphology, for the samples grown under O reduced conditions. Relative O contents are estimated using electron energy loss spectroscopy studies. Size-selective growth of uniform nanowires is also demonstrated, under the O reduced condition, using different catalyst sizes. Photoluminescence studies along with the observation of single-mode waveguide formation, as far field bright violet multiple emission spots, reveal the high optical quality of the nonpolar GaN nanowires grown under the O reduced condition.