The morphology and mechanical properties of non-reactive and reactive polyamide (PA)/polysulfone (PSU) blends prepared in a mini-twin screw extruder and a Haake batch mixer were investigated and compared using transmission electron microscopy and solvent extraction. In the reactive blend, few wt.% of phthalic anhydride-terminated PSU was added. The new mini-twin screw extruder, allowing the compounding of laboratory products starting from 150 g, is efficient in producing homogenous dispersion in both non-reactive and reactive PSU/PA blends. In the reactive systems, PSU-PA copolymers in situ formed act as typical emulsifier to provide finer particle size and better morphology stability. Significant toughness improvement found in the reactive systems appears to originate from the enhanced interfacial adhesion provided by the PSU-PA copolymers, not simply by the reduced particle size of PA dispersed phases.