Aqueous solutions of the graft copolymer with a polyimide backbone and poly(N,N-dimethylamino-2-ethyl methacrylate) side chains with a molecular mass of M = 4.7 × 10⁵ and a grafting density of side chains of 0.44 are investigated by light scattering and turbidimetry. Solutions are studied in a wide concentration range of 0.0008–0.0250 g/cm³ at рН values varying from 2 to 12 for each concentration. The temperature dependences of optical transmission, scattered light intensity, and hydrodynamic radii of scattering objects are obtained. It is shown that the copolymer is thermosensitive only at pH > 8.0. A decrease in acidity of the medium at a fixed concentration of the copolymer is accompanied by a decline in temperatures corresponding to the onset and end of phase separation Т₁ and Т₂, leading to the narrowing of this interval. At constant рН values, temperatures Т₁ and Т₂ rise with solution dilution, while the phase transition interval becomes wider.