Ordering process of lamellar microdomains of poly(styrene‐block‐butadiene‐block‐styrene) (SBS) triblock copolymers in melts has been studied using small‐angle X‐ray scattering (SAXS). The SAXS profiles were analyzed by means of the theoretical calculation based on the one‐dimensional paracrystal model so as to characterize quantitatively how the lamellae which were formed through coalescence of cylindrical microdomains ordered. As a result of the analysis, it was found that the distribution of the interlamellar distance and the thickness distributions of polystyre (PS) and polybutadiene (PB) lamellae decreased, whereas the interlamellar distance and the interfacial thickness did not definitely change with time.