Twin screw extruders (TSEs) normally are used when the application of high stresses and long residence times in the polymer melts is necessary, especially in polymer blending and compounding. In order to achieve a uniform dispersion of the second phase in the matrix high levels of dispersive and distributive mixing are needed leading to high performance properties in blends. However, the effect of process conditions along the extruder barrel can significantly change the dispersion and distributive condition of the melt during its processing especially when it comes to reactive extrusion. The goal of this work is to develop and validate the On-line Fourier transform infrared spectroscopic set-up for the real-time quantification of the melt extrudate during reactive extrusion-based process. The arrangement consists of an infrared spectrophotometer operating in attenuated total reflectance ATR-FT-IR, fitted on-line, along the extruder barrel. The setting helps to understand the effect of extrusion process parameters and the reaction conversion during development of polymer blends and compound in-processing. The ATR-FT-IR spectroscopic probe has been coupled along with an extruder to analyze/understand the process during operation in the MID region of the infrared spectrum. The ATR-FT-IR prototype probe was calibrated and validated using off-line measurements. The probe is interfaced to the extruder through to a probe holder unit (PHU). The on-line ATR-FT-IR measurements were conducted at various locations (L/D) along the length of the extruder. Polymer blends of PP/PA6 in various compositions were investigated and reactive blends on PP-g-AA/PA6 were used to validate the on-line measurements compared to the standard off-line ATR-FT-IR and transmission analyses.