Nanoparticles of ZrN, ZrO2 and b'-Zr7O11N2 were synthesized by pulsed wire discharge using Zr wire in various O-2 and N-2 gas mixtures with different oxygen partial pressures of up to 40 kPa and a total pressure of 100 kPa. The syntheses were carried out at a relative energy ratio (K) of 6.4 which was defined by a charged energy in a capacitor of the synthesis apparatus divided by the evaporation energy of the Zr wire. Morphology and phase analyses were carried out on these nanoparticles by X-ray diffraction and field-emission transmission electron microscopy. ZrN and Zr2N were observed in a sample synthesized in 100% N-2 gas while with increasing the O-2 from 1% of total pressure, formation of b'-Zr7O11N2 and ZrO2 was seen. By bright field image observation, electron energy loss spectroscopy (EELS) and selected area electron-diffraction analyses, nanoparticles of ZrN, b'-Zr7O11N2 and ZrO2 were separately characterized. In these syntheses, nanoparticles of b'-Zr7O11N2 existed in much smaller size and different shape than the ordinary spherical nanoparticles of ZrN and ZrO2. In gas mixtures where O-2 contents were larger than 22% (dry air composition), ZrN was not detected or detected with just a fractional amount compared to the two major phases of b'-Zr7O11N2 and ZrO2. EELS data for ZrN and b'-Zr7O11N2 were obtained and compared by separated analyses of nanoparticles of these phases. From these data, it was concluded that, in nuclear accidents, small amount of particles can indicate the accident atmosphere around the Zr alloys fuel cladding.