ABS/PMMA binary and ABS/PMMA/PC ternary blends were prepared using a corotating twin screw extruder. Blend samples were annealed in a constrant temperature(215 and $225^{circ}C$) hydraulic press up to 85min. The changes of morphology and mechanical properties with annealing time were studied with TEM, image analyzer, and tensil tester. With the increase in annealing time, the number of ispersed domains per corss-sectional area decreased, and average domain size increased, and this morphology coarsening became more responsible with time for the deterioration of blend properties. In ABX/PMMA/PC ternary blends, PMMA encapsulated PC in ABS marix, and this was predictable from the spreading coefficinet calculation.