The crystal structures of thermoelectric (TE) compounds Bi 1.91Sr2.0Rh1.77Ox and Bi 2.12Ba2.00Rh1.95Ox are investigated by means of electron diffraction measurements and high-resolution electron microscopy. These compounds have layered structures and consist of two interpenetrating subsystems exhibiting incommensurated periodicities along b-axis. Both subsystems, CdI2-type RhO2 sheets and a distorted four-layered rock-salt (RS)-type (Bi,(Sr,Ba))O blocks, have common a-, c-axes and β-angles. On the other hand, the ratios of two axis lengths, i.e., b1 (RhO2 sheet) / b2 (RS-type block), are irrational. Based on the cation ratio and b1/b2 value, the structural formulae are expressed as [(Bi1-xRhx) 2(Sr1-yBiy)2O4+δ] 0.63RhO2 with x=0.077, y=0.016 and δ=0.46 for the Sr-system and [(Bi1-xRhx)2(Ba 1-yBiy)2O4+δ] 0.56RhO2 with x=0.037, y,=0.047 and δ=0.39 for the Ba-system, respectively. Based on the electron diffraction measurements, it is found that these compounds have irrational modulation vectors, q1 = - a* + 0.63b1* and q2 = 0.17b1* + c for Bi-Sr-Rh-O, and q1 = - a* + 0.56b1* and q2 = 0.11b1* + 0.35c* for Bi-Ba-Rh-O, respectively, being the indications of (3+2) dimensional structures. High-resolution images taken with the incident electron beam parallel to the a- and c-axes clearly exhibit modulated atomic arrangements. These compounds are characterized by the displacement modulations in both RhO2 layers and the RS-type blocks.