Wetting of ZrO2-3 mol% Y2O3 substrates by a molten Zr55Cu30Al10Ni5 bulk metallic glass forming alloy was studied using a modified sessile drop method at 1133-1473 K in a high vacuum and their interfacial chemistry was investigated. The time variation in the contact angle shows anomalous temperature dependence at 1133-1293 K, i.e., the initial contact angle gradually decreases while the final contact angle increases with increasing temperature. In the range of 1293-1473 K, the contact angle sharply decreases in the initial stage but shows little change in the subsequent long isothermal duration. A distinct reaction layer consisting of substoichiometric ZrO2-x was developed at the interface. The remarkable temperature dependence of the wettability is due to the competition among the adsorption and accumulation of the active atoms such as Zr at the interface, the interfacial reaction, and the release of oxygen from ZrO2. The adsorption of Zr at the triple junction, particularly enhanced by the structural transition of ZrO2, plays an important role in promoting the wettability. In contrast, the oxygen release leads to the oxidation of the active atoms and ready pinning of the triple line, thus deteriorating the wettability. The interfacial reaction may promote the wetting as well, but its role is limited because on the one hand, it consumes the adsorbed active Zr atoms, and on the other, the pinning of the triple line due to the compositional oxidation considerably weakens its function.