In this paper, diphenyl-silsesquioxane was synthesized and characterized. Firstly, octa-isobutyl silsesquioxane endo-disilanol (OIBS-EDN) containing two Si-OH functions was formed by base-catalyzed cleavage of octa-isobutyl silsesquioxane (OIBS). Then, oligomeric silsesquioxane containing two phenyl functions (DPS) was prepared by adding diphenyldichlorosilane to the solution of OIBS-EDN in right proportion with the presence of trithylamine in THF. The products were characterized by FTIR, 1HNMR, 13CNMR, 29SiNMR, X-ray diffraction, EA, DSC and GPC respectively. The results show that difunctional POSS with clear structure and high yield can be prepared by this process. And a new simple and feasible approach to design and synthesize difunctional POSS was put forward.