The phase behavior of binary blends of symmetric long diblock copolymers and nearly short symmetric diblock copolymers with different ratio of chain lengths is studied using the self-consistent field theory.The occurrence of order-order transition

disorder-order transition and regions of order-disorder coexistence has been examined.Comparisons are also made with the theoretical study of the binary blend of symmetric long and short diblock copolymers and experiments on the similar systems.The effects of the short nearly symmetric diblock copolymer on the symmetric long diblock copolymer in their blends were analyzed.