The separation of Mo(VI) and W(VI) from sulfate solution by LIX 63 and PC 88A was investigated as a function of solution pH. Using LIX 63, selective extraction of Mo(VI) over W(VI) in the initial pH range from 2.0 to 6.0 was achieved and a separation factor of 406 was obtained. However, it was impossible to separate Mo(VI) and W(VI) by extraction with PC 88A in the same pH range. The equilibrium pH was higher than the initial pH, suggesting a possible solvating mechanism. The loaded Mo(VI) was quantitatively stripped from the loaded LIX 63 and it was possible to obtain a Mo(VI) solution with purity of 99%. The McCabe–Thiele diagrams for the extraction and stripping of Mo(VI) by using LIX 63 were constructed.