The order-disorder transition (ODT) and the ordering kinetics have been studied in two symmetric diblock copolymers of styrene and isoprene and their binary mixtures with theology. The binary mixtures formed a single microdomain (with lamellar morphology) composed of short and long chains as confirmed by small angle x-ray scattering (SAXS). The order-disorder transition temperature (T-ODT), obtained from the discontinuity in the storage modulus G’, varies linearly with the number average degree of polymerization. For shallow quenches, the ordering kinetics proceed via nucleation and growth. The characteristic time of this process scales with (N) over bar(-1/3), where (N) over bar is the Ginzburg parameter, in agreement with the theoretical predictions [G. H. Fredrickson and K. Binder, J. Chem. Phys. 91, 7265 (1989)]. Our results indicate that the ordering kinetics of symmetric diblock copolymers near the ODT are fluctuation controlled.