ZnSe/$SiO_2$ coaxial nanowires were synthesized by a two-step process: thermal evaporation of ZnSe powders and sputter-deposition of $SiO_2$. Two different types of nanowires are observed: thin rod-like ones with a few to a few tens of nanometers in diameter and up to a few hundred of micrometers in length and wide belt-like ones with a few micrometers in width. Room-temperature photoluminescence (PL) measurement showed that ZnSe/$SiO_2$ coaxial nanowires had an orange emission band centered at approximately 610 nm. The intensity of the orange emission from the $SiO_2$-sheathed ZnSe nanowires was enhanced significantly by annealing in a reducing atmosphere whereas it was degraded by annealing in an oxidizing atmosphere. The origins of the PL changes by annealing are discussed based on the energy-dispersive X-ray spectroscopy analysis results.