Examination was made of changes in volume of 2-(acryloyloxy)ethyl acid phosphate (AEAP)/acrylamide copolymer gel immersed in acetonitrile-water, methanol-water, tetrahydrofuran-water, dioxane-water, and dimethyl sulfoxide-water. The gel underwent reversible volume change from a swollen to a collapsed state via a discontinuous volume change with an increase in solvent composition, and the discontinuous volume change at the transition point decreased with an increase in AEAP content. The transition point shifted first toward lower solvent content and then higher solvent content. This was a newly observed volume phase transition which was a combination of normal pattern and : specific pattern recently found by us. This type:of volume phase transition was characterized by the fact : that phase transition threshold, i.e., threshold solvent composition, varied with polymer composition in a non-monotonic way. This transition could be considered consistent with nonlinear change in miscibility of the gel polymer in solvent mixtures, that is, first increasing and then decreasing with an increase in AEAP.