As YBCO oxide superconductor has high critical temperature and high critical magnetic field, a great deal of research has been conducted due to great potential applications. The evaluation of the mechanical property of YBCO system is therefore important in addition to superconducting properties. However such studies are few, and the fracture mechanism of YBCO has not been investigated. In this paper, the Brazilian test and cyclic loading tests were performed in liquid nitrogen to evaluate the microfracture behavior of YBCO superconductor by use of SQUID (Superconducting QUantum Interference Devices). Initiation and extension of cracks can be detected by use of SQUID as variation in the magnetic field caused by cracks under applied current. The sign of SQUID signal indicates the cracking location, because the sign depends on the location of cracks and sensing coil of SQUID.