A comparative experimental study of soft x-ray emission from laser-irradiated Au–Cu mix-Z targets of different atomic compositions has been performed. Plasma was produced from planar targets using second-harmonic laser pulses from an Nd:glass laser at a focused intensity of;10¹³ W cm^-2. Radiation intensity in the spectral region ~15-150 Å and integrated x-ray yield for mix-Z target were observed to be higher than those for individual elements. The maximum conversion occurred for an atomic composition of Au 0.43–Cu 0.57. These observations are consistent with the variation of Rosseland mean opacity with atomic composition calculated using a screened hydrogenic average atom model.