We present the direct observations of microstructure with clustering by electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) oil cluster-glass (CG) magnetic compounds R2CuSi3 (R = Ce and Nd) related to a hexagonal AIB(2)-type structure. Observed diffraction patterns show Superstructure reflections at 1/2 1/2 1/2-typed positions, which are very similar to the results observed for the CG compound U2IrSi3. Fourier-filtered HRTEM images clearly exhibit a domain structure. The size of the domains with a base-centered ordering Structure in Ce2CuSi3 is estimated to be 2-3 run in much smaller than that in Nd, CuSi3. These observations are consistent with the inferences based on the magnetic measurements, and can be considered as the direct evidence for the formation of magnetic cluster in Ce2CuSi3 and Nd2CuSi3. (C) 2008 Elsevier Ltd. All rights reserved.