Mycobacterial cell wall consists of rigid cell wall skeleton (CWS), a mycoloyl arabinogalactan peptidiglycan complex, in which mycoloyl structure varies by the mycobacterial species diversely, whereas the arabinogalactan peptidoglycan structure is consistent comparatively. The CWS of Mycobacterium bovis BCG has long been expected as a potent adjuvant for immunotherapy of malignant tumor. Although the chemical structure of CWS has been established in the last few decades, the physicochemical properties of CWS having highly amphipathic micelle structure with very long mycoloyl and carbohydrate chains are not unveiled. In this study, the ultrastructure of CWS of M. bovis BCG Tokyo 172 (SMP-105), suspended in several solvents with different polarity, was investigated with a particle size analyzer, a transmission electron microscope (TEM) and other techniques. As a result, the particle size was about 4.7 to 67.8 microm in physiological saline, but it became smaller and more compact when suspended in hydrophobic solvents. TEM images showed two different morphological forms distinctively: double folded sheet structure in hydrophilic conditions and multilayered rolled sheet structure in hydrophobic conditions. These studies have revealed characteristic surface features of SMP-105, the hydrophobic moiety occupying dominant space and the hydrophilic moiety smaller space, respectively, which may lead to the acceleration of immunological studies on this product.