Exploring the novel application to the quantum optics, the periodic crystallographic-polarity-inverted GaN waveguides were fabricated. In addition to the successful periodic reversal of the crystallographic orientations, periodic grating structures were formed on the surface due to the slight difference in the growth rates for different polarities, which gives the occurrence of the well-known photonic band structures. In this work, basic optical properties were investigated utilizing the variable-angle optical reflectance measurements on these waveguides with one-dimensional periodic grating structures, in order to obtain their photonic band structures. In addition to the optical interference fringes, clear reflectance dips originated from the resonance between the incident light and allowed waveguide modes appeared, aside from a weak resonant feature due to the coupling of the diffracted light to the evanescent mode on the grating surface, known as Wood's anomalies. Taking into account the refractive index dispersions and the zone-folding effects invoked by the grating, the origins of all the resonant features are successfully elucidated. Especially in case of resonant coupling to the waveguide modes, the corresponding orders of both the grating diffractions and the guided modes are assigned. Based on these assignments, the possible configurations of the wavelength conversions are discussed.