Abstract: Total ionizing dose effects by cobalt-60 and the following room temperature annealing behaviors of a 16 Mb commercial Magnetoresistive Random Access Memory（MRAM） are experimentally evaluated. DC, AC and function parameters of the memory during and after irradiation were tested by Verigy93000 chip Automatic Test Equipment（ATE）. Radiation-sensitive parameters were given. According to variation trends of sensitive parameters, the physical mechanism of total ionizing dose effects and annealing characteristics of MRAM were analyzed in detail. It is shown that the large quantity of trapped charge in the structure of Shallow Trench Isolation（ STI） oxide, generated by ionizing radiation, is the main reason to degrade memory performance. The large number of oxide-trapped charge recombined with the electrons coming from silicon substrate in room temperature is annealing, and gradually disappears. That’s why the functions and electrical parameters of MRAM were recovered quickly. The experimental data and analysis in this work are useful for radiation-tolerant MRAM development aiming at space applications.