High quality factor a-plane nonpolar GaN two-dimensional photonic crystal (PC) nanocavities on r-plane sapphire substrates have been demonstrated. Nonpolar GaN PC nanocavities on a thin membrane structure were realized by using e-beam lithography to define the PC patterns and focused-ion beam milling to fabricate the suspended thin membrane. A dominant resonant mode at 388 nm with a high quality factor of approximately 4300 has been demonstrated at 77 K by the micro-photoluminescence system. Moreover, the degree of polarization of the emission from the non-polar GaN PC nanocavity was measured to be 64% along the m crystalline direction.