Surface tension of liquid Ag-Cu binary alloys has been measured contactlessly using the technique of electromagnetic levitation in combination with the oscillating drop technique. The measurements were performed at temperatures above the melting point of alloys. The surface tension values were obtained from an analysis of the frequency spectra of droplet oscillations recorded with a CMOS-camera at 400 fps.The alloy samples covered the entire composition range. The surface tension data can be described by linear functions of temperature with negative slopes. The new experimental data were compared to the corresponding theoretical values calculated combining the Butler equation with the ideal and subregular solution models, respectively. The agreement with the experimentally obtained data is excellent for the isothermal surface tension and quite reasonable for their temperature coefficients.