A series of the copolyimides have been synthesized by one-step high-temperature method in m-cresol solution to explore their effect on the optical fibre coatings formation and properties. The following parameters that influence the coating quality and properties have been estimated: the viscosity of the polymer solution, drawing technological parameters, polyimide (PI) structure and molecular weight. It was found that copolyimides bearing side hydroxyl and carboxyl groups formulate the coatings with good adhesion without additional coupling agent. The fibres with elaborated PI coatings have high thermal stability. For some of them, 20% reduction of the fibre’s bending strength takes place only after heating for 24–72 h at 300°C.