Crystallization temperature (Tc)-dependent crystal orientations within nanoconfined lamellae have been studied in a self-assembled poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer. The copolymer possesses number-average molecular weights of MnPEO = 8.7K and MnPS = 9.2K, and it forms a microphase-separated lamellar structure in the melt. It has been found that the PEO crystal (the c axis) orientations are determined by only varying the Tc.1 Based on real-time simultaneous two-dimensional (2D) small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) experiments, the formation of crystal orientation is found in an early stage of PEO crystallization confined between the PS lamellae. To understand whether the crystal orientation is determined during the primary nucleation or crystal growth step, specifically designed self-seeded crystallization experiments are carried out using 2D SAXS and WAXS techniques. Experimental results suggest that primary nuclei (self-seeds) do n...