Summary: A process for the production of poly(butyl methacrylate) optical fibers by reactive extrusion is developed. The reactive system is adapted to the reduced reaction time in the extruder combining concepts based on the free volume theory and a kinetic model for the mass polymerization of butyl methacrylate. A kinetic model is proposed and the reaction evolution is simulated at different temperatures and initiator concentrations. This allows the choice of reaction conditions adequate for reactive extrusion technical limitations. Reactive extrusion experiments are carried out in a twin‐screw extruder and the effect of the different kinetic and process conditions on the reaction are analyzed in relation to the residence time distribution measured by an UV fluorescence method. Some optical properties of poly(butyl methacrylate) fibers are reported.