We revealed the aggravated instability of (0001)-oriented ZnO nanowires when they were deposited by a TiO(2) shell even under ambient conditions. Trace UV photons from daylight and moisture from air, which generally have negligible effects on "bare" ZnO nanowires, can obviously enhance their photocorrosion due to the high bandgap of TiO(2) as well as this conformal core-shell heterostructure.