The sintering behavior, superconductivity, and microstructure of the YBa2-xCsxCu3O7 system has been investigated. The Tc measurements indicate that the Cs addition inhibits the sensitivity of the superconducting phase to oxygen activity. Thus, the superconductivity can be observed in samples sintered in a wide range of temperatures from 850” to 1200°C. XRD results show that Tc increases along with an increasing lattice parameter ratio(b/a), implying that the higher Tc superconduching specimen possesses a more fragile structure. This phenomenon can be correlated to the quantity as well as the width of twins observed in the TEM micrographs.