Abstract Various properties of W Cu solid solutions are systematically investigated through a combined use of first-principles calculation, cluster expansion, special quasirandom structures (SQS), and lattice dynamics. It is shown that SQS are effective to unravel the intrinsic nature of solid solutions, and that BCC and FCC W 100-x Cu x solid solutions are energetically more stable when 0 ≤ x ≤ 70 and 70 Cu, and that the coefficients of thermal expansion of W 100-x Cu x solid solutions are much lower than those of corresponding mechanical mixtures. In addition, the G/B values of W 100-x Cu x solid solutions reach a minimum at x = 50, which is fundamentally due to the softening of phonons as well as strong chemical bonding between W and Cu with a mainly metallic feature.