The development of phase morphology in non-reactive vs reactive polyamide blends with a styrene-acrylonitrile (SAN) copolymer and SEES (a styrenic triblock copolymer with ethylene-butylene midblocks) in a co-rotating twin screw extruder was investigated using electron microscopy techniques. For the polyamide/SAN systems, significant differences were observed between the evolution of morphology in non-reactive binary blends vs blends compatibilized with a reactive imidized acrylic (IA) polymer which is miscible in the SAN phase and has functional groups which are capable of reacting with the amine end groups in the polyamide phase. While a steady decrease in the dispersed phase particle size was observed in general for the non-reactive nylon 6/SAN blends with both increasing screw length and speed, for the ternary nylon 6/SAN/IA blends a dramatic drop in the dispersed phase particle size was observed in the initial region of the screw almost immediately after melting of the pellets followed by some coalescence of dispersed phase in the latter stages leading to a dual population of particle at the exit of the extruder. The extent and onset of coalescence after attainment of minimum particle size in the initial region of the screw in reactive nylon 6/SAN blends was found to be strongly dependent on the screw speed and configuration. The extent of chemical reaction along the extruder screw for reactive nylon 6/SAN blends was dependent on the screw speed, extruder configuration and flow rate. While similar differences in the evolution of morphology were observed between non-reactive and reactive polyamide/SEBS systems, changing the polyamide type from monofunctional (nylon x, e.g. nylon 6) to difunctional (nylon x, y, e.g. nylon 6,6) revealed interesting differences even within these reactive blends. Significant differences in both the development of morphology and reaction profile along the screw were also observed between binary and ternary nylon 6/rubber blends containing similar concentrations of reactive maleic anhydride functionality in the rubber phase using a fixed screw speed and configuration.