A new kind of polysiloxane containing N,N ' -bis(diphenylsilyl)tetraphenyl-cyclodisilazane was prepared by the anionic polymerization with a "Seed solution" as initiator. The synthesis of monomers N,N ' -bis(hydroxydiphenylsilyl)tetraphenylcyclodisilazane (BHPTPC), N,N ' -bis(chlorodiphenyisilyl)tetraphenylcyclodisilazane (BCPTPC), and 1,3-dichloro-1,1,3,3-tetraphenyldisilazane (DCTPS) are all reported in this study, The synthesized polysiloxane containing N,N ' -bis(diphenylsilyl)tetraphenylcyclodisilazane was characterized by H-1-NMR, Si-29-NMR, gel permeation chromatography (GPC), and intrinsic viscosity. The thermal stability of the polysiloxane was studied by isothermal gravimetric analysis (IGA). The results demonstrated that the synthesized polysiloxane containing N,N ' -bis(diphenylsilyl)tetraphenylcyclodisilazane had excellent thermal stability.