The geometrical structures and relative stability of the various possible isomers of silicon-oxygen-sulfur oligomers, (SiOS)n (n=1-6), were studied using quantum chemistry calculations. The linear monomer with Si atom bonding to both O and S atoms is the ground state isomer, and the rhombic chains of four-membered rings are the most stable configurations for n=2-4, while the hybrid structures by the 4MRs and hexagonal six-membered ring become energetically most favorable for n=5 and n=6. Vibrational frequency calculations show that the characteristic IR signatures occur at 1290cm 1 for n=1, at the vicinity of 900cm forn=2-4, and at about 1080cm 1 for n=5-6. These distinctive spectra would provide guide for future experimental detections of these small Si-O-S oligomers.