The surface tensions gamma of liquid Al-Au binary alloys are measured contactlessly using the oscillation drop technique of electromagnetic levitation. Data are obtained in experiments performed on ground and in micro-gravity during a parabolic flight campaign. For all samples and for all compositions, the surface tension decreases linearly with temperature. At 1400 K, gamma monotonously decreases with increasing Al concentration. Features of compound formation, such as a maximum in the isothermal surface tension, are not evident from the experimental data. The results are in good agreement with the Butler and the Chatain model both using the sub-regular solution approximation.