X-ray diffraction measurements under pressure have been performed on seven different compositions in the UxLa1-xS system (x = 0, 0.08, 0.40, 0.50, 0.60, 0.80, 1). All the compounds have the same structure (NaCl type) at ambient pressure, but show different behaviours under pressure. A transformation into the CsCl-type structure is only observed for x ≤ 0.60. For x = 0.80 and 1, the high-pressure phase has yet to be determined. We also observe a difference in bulk modulus (for x ≤ 0.50, B0 ≤ 90 GPa whereas for x ≥ 0.60, B0 ∼ 100 GPa) and in the transition pressure (∼30 GPa for low-uranium-content compounds and from 45 to 80 GPa for high concentrations).