With the combination of various in-situ surface science tools, surface chemical and structural properties of bimetallic AuPd(1 1 0) alloys are characterized under elevated CO pressure. Under 1 Torr of CO gas pressure, STM images show the formation of nano-sized surface rice-grains along the index direction of [1-10] while PM-IRRAS shows new CO vibrational band. This new vibrational band of PM-IRRAS is confirmed as the CO molecules attached to atop site of Pd with the results of ambient pressure XPS. In the case of adsorption of CO on AuPd(1 1 0) alloys, the so-called "pressure gap" exists and the surface morphology and its chemical states change at elevated pressure conditions. (C) 2015 Elsevier B.V. All rights reserved.