Abstract: Objective: To study the post-radiotherapeutic effect on the memory of the patients with nasopharyngeal carcinoma and to explore the feasibility of memory detection as the method for early discovery of radioactive brain injury. Methods: Memory test was used to assess the memory quotient (MQ) of 61 patients with nasopharyngeal carcinoma before and after radiotherapy, and 20 patients were examined by CT or MRI concurrently. Results: In the 61 cases, 18% of them (11/61 cases) were those with bad or worst MQ, 29.5% (18/61) were with the lower-middle MQ, 39.3% (24/61) were the middle, 8.2% (5/61) were the higher-middle, 3.3% (2/61) excellent, 1.6% (1/61) very excellent. There was a close relationship between the MQ and the irradiation dose in.9 of the 11 cases, whose MQ was bad or worst, with the dose over 70 Gy. The MQ of 6 patients was lower than 89 scores (which belonged to the grade of lower-middle or worse ) and the 6 were among the 8 cases (75.0%) treated by radiotherapy again for recurrence. There was a significant relationship between the level of MQ and the degree for cerebral atrophy and encephalomalacia. CT or MRI showed cerebral atrophy occurred in 12 cases and encephalomalacia in 8 (all at the bottom of temporal lobe bone) in the 20 cases whose MQ was lower than 89 scores. There is no significant difference between the grade of MQ and the survival time after radiotherapy. Conclusion: Memory test is a valuable tool to detect and diagnose brain injury to the patients with nasopharyngeal carcinoma after radiotherapy.