Magnesia (MgO) either intrinsically contained in cement clinker or prepared separately as expansive additive has been used to compensate for the shrinkage of cementitious materials. In this study, for improving the homogenous distribution of MgOs, the cement clinker was inter-ground with MgO expansive additives with various reactivities ranging from 50 to 400 s to prepare series of expansive Portland cements and blended cements with incorporation of slag and fly ash. The deformations and mechanical properties of the expansive cements were investigated. Results showed that the expansive cements containing more reactive MgOs produced more rapid expansion under sealed condition or water curing, leading to effective autogenous shrinkage compensations at early age. The reactivities of MgOs caused insignificant influences on the mechanical strengths of expansive cements. The blended cements had lower strengths at early age but higher strengths than that of the corresponding Portland cements at late age due to the pozzolanic reaction.