The present application describes a modular unit for injection-compression molding (1). The modular unit for injection-compression molding (1) is arranged between the movable platen of the injection machine (21) and the stationary platen of the injection machine (22), in particular in the half-mold bearing face resulting from the division thereof by the opening joint. This modular unit for injection-compression molding (1) allows a substantial reduction of energy spent by reduction of inertial masses involved. The present application describes a modular unit for injection-compression molding (1) to be used in the production of pieces by injection being installed on any thermoplastic molding process.