Acrylonitrile-butadiene-styrene terpolymer (ABS)/poly(methyl methacrylate) (PMMA) binary and ABS/PMMA/polycarbonate (PC) ternary blends were prepared using a corotating twin-screw extruder. Blend samples were annealed in a constant-temperature (215 and 225 degrees C) hydraulic press up to 85 min. The changes in morphology and mechanical properties with annealing time were studied with transmission electron microscopys image analyzer, and tensile tester. With the increase in annealing time, the number of dispersed domains per cross-sectional area decreased and average domain size increased; this morphology coarsening became more responsible with time for the deterioration of blend properties. In ABS/PMMA/PC ternary blends, PMMA encapsulated PC in ABS matrix; this was predictable from the spreading coefficient calculation.