With the advent of system-on-chip (SOC), the demand for embedded memory cores increases rapidly. The Magnetic Random Access Memory (MRAM) is considered one of the potential candidates that will replace current on-chip memories (RAM, EEPROM, and flash memory) in the future. The MRAM has a high speed and does not need high supply voltage for Read/Write operations, so it has the advantages of RAM and flash memory, making it a potentially good choice for SOC. The testing of MRAM, however, has not been fully investigated. In this work we classify and analyze the MRAM defects and their behavior, and propose its fault models. We have built a SPICE model of MRAM cell and performed defect injection and simulation of a real MRAM circuit. The circuit has been implemented and fabricated with a novel 0.18?m technology. The simulation results regarding the correlation between the defects and conventional fault models show that most of the defects can be covered by the stuck-at fault model. The test data based on the fabricated chips show that the stuck-at faults do cover most of the defects on the chips. However, from the experiment we also have identified two new faults, i.e., the Multi-Victims fault and Kink fault.