Abstract: Objective To investigate the clinical value of ^99mTc-4, 9-diaza-3, 3, 10, 10-tetramethyldodecan-2, 11-dione dioxime(^99mTc-HL91) hypoxia imaging in detecting radiotherapy response of nasopharyngeal carcinoma. Methods Thirty patients with nasopharyngeal carcinoma who will receive radiotherapy underwent ^99mTc-HL91 imaging at lh and 4 h post-injection of ^99mTc-HL91. Region of interest technique was used to calculate the tumor-to-background ratios of scalp(T/B). The effects of radiotherapy were evaluated 4 weeks later by the radiotherapists according to the standard of WHO. Results ① The ^99mTc-HL91 uptake ratios of T/B in thirty patients at 1 h and 4 h imaging were 1.370±0.207 and 1.883±0.358, respectively. There was a significant difference between T/B value of the two phases (t=6.794, P<0.001). ② The follow-up results demonstrated that the average T/B value at lh and 4 h phase in the group of effective radiotherapy and ineffective radiotherapy were 1.273±0.196 and 1.498±0.147, 1.679±0.232 and 2.152±0.318, respectively. There was a significant difference between T/B value of the two group. Conclusion The hypoxia status can be observed by ^99mTc-HL91 imaging which has certain clinical value in forecasting the effects of radiotherapy.