The effects of copolymer architecture on phase separation dynamics of an immiscible binary blend A/B in the presence of copolymer were investigated by Monte Carlo simulation. Five types of copolymers, with each having the same composition (f = 0.5) but different sequence distribution, are used for simulation. The sequence distribution is varied from the symmetric diblock copolymer to the alternating copolymer. It is found that the rate of phase separation is significantly suppressed by the addition of copolymer due to the reduction of interfacial tension. This retardation effect is considerably dependent on the sequence distribution of the copolymer and such an effect is more pronounced when the block copolymer is added. It is also found that the longer the chain length of copolymer, the better such a retardation effect. When the chain extension of copolymer at the interface is examined, the block copolymer chains are extended to each corresponding homopolymer phase across the interface, whereas the alternating copolymers lie on the interface and the random copolymers weave back and forth across the interface.