AbstractLiquid‐vapour equilibrium data for methyl methacrylate‐methanol and methyl methacrylate‐methacrylic acid mixtures have been determined using a modified Rosanoff apparatus at 200 mm. and 760 mm. Hg pressure. It has been found that methyl methaerylate forms constant‐boiling binary mixtures both with methanol and with water. Some physical properties of pure methyl methaerylate and mixtures with water, methanol and methacrylic acid have been det