The compressions at 25� of dioxan-water mixtures containing 0, 25, 50, 70, 80, and 100 wt.% dioxan have been determined at pressures up to 1500 bars. The mixtures show a minimum compression at a composition between 25 and 50 wt.% dioxan. The freezing pressure of dioxan at 25� is estimated to be 625 bars but measurements have been made on the metastable liquid at pressures up to 960 bars.