In this study, carbosilane-based oligomers with tetraallylsilane in the core whose periphery was modified with side-on type mesogenic groups were synthesized with systematic change in the spacer length. The results obtained by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) revealed that the oligomers exhibited nematic phases near room temperature. Furthermore, a nematic liquid crystal containing 20 wt% of each oligomer exhibited spontaneous homeotropic alignment in the non-treated glass cells.