Abstract: Total ionizing dose (TID) and single event effect (SEE) are both the main threats to nano-SRAMs devices in space application. With the development of CMOS technology, some new phenomena were observed during studying the synergistic effect between TID and SEE on nano-SRAMs. γ ray and heavy ion irradiations were performed to investigate the impact of total ionizing dose on single event upset (SEU) sensitivity of SRAMs. The influence of irradiation parameters, test modes and data patterns on synergistic effect were studied. The results showed that γ ray irradiation led to the decrease of threshold voltage and the increase of leakage current of inverters, which reduced the SEU hardness of SRAMs. Meanwhile, the SEU cross section increased compared with that of non-TID irradiated devices. There was no significant change in the percentage of multiple-bit upset (MBU). No "imprint effect" was observed. Data pattern applied in TID and SEE tests had no influence on the test results of SEU cross section.