Temporal universal conductance fluctuations (TUCF's) are observed in RuO 2 nanowires at cryogenic temperatures. The fluctuations persist up to very high T ∼ 10 K. Their root-mean-square magnitudes increase with decreasing T , reaching ∼ 0.2e 2 /h at T 2 K. These fluctuations are shown to originate from scattering of conduction electrons with rich amounts of mobile defects in artificially synthesized metal oxide nanowires. TUCF characteristics in both one-dimensional saturated and unsaturated regimes are identified and explained in terms of current theories. Furthermore, the TUCF's as a probe for the characteristic time scales of the mobile defects (two-level systems) are discussed.