Ordering of cylindrical microdomains in a low molecular weight polystyrene-block-polyisoprene (SI diblock) copolymer was investigated using small-angle X-ray scattering (SAXS) and theology. The SI diblock copolymer was found to have (i) hexagonally packed cylindrical microdomains of polystyrene phase in a polyisoprene matrix in the ordered state, and (ii) an order-disorder transition temperature T-ODT Of Ca 90 degrees C. TO investigate the ordering process from the disordered state, a specimen was quenched rapidly from the disordered state to a temperature below its T-ODT, and then the time evolution of the SAXS intensity and dynamic moduli (G＇ and G ") (i.e. the ordering process) was monitored. We have found that the ordering process in the block copolymer, when quenched to an ordered state close to its T-ODT. takes place very slowly. Specifically, we found that when a specimen was quenched rapidly from 100 degrees C (10 degrees C above T-ODT) to 80 degrees C (10 degrees C below T-ODT), the ordering into the hexagonally packed cylinders occurs via a nucleation-growth process and the attainment of the equilibrium microdomain morphology took about 6 h when monitoring G＇ and G " and about 8 h when monitoring the SAXS intensity.