Pre-ceramic polymers, notably, polysiloxanes, etc., are ideal materials for complex 3D- printed ceramic materials structures, via a direct ink writing process, followed by curing and pyrolysis. The resulting silicon carbides and silicon oxycarbides with precisely engineered architectures have abroad engineering applications, because of their extraordinary mechanical and physical properties. To achieve high quality ceramic structures, proper curing of pre-ceramic polymers is crucial, aiming at the highest possible crosslinking density. In the meantime, a mild crosslinking process with uniform crosslinking and absence of cracking is preferred. To achieve these objectives, the crosslinking characteristics of polysiloxanes need to be well understood for finding the desirable curing conditions. In this study, parallel plate rheometer was used to study crosslinking behaviors of polysiloxanes catalyzed by Karstedt's catalyst. The changes of viscoelastic properties upon crosslinking were analyzed to uncover the time and temperature characteristics of such crosslinking processes. The characteristic crosslinking temperature, i.e. the temperature for the fastest property changes, is determined.