Objective: The purpose of the study was to evaluate clinical value of dual-phase $^{18}F$-FDG SPECT with serum procalcitonin (PCT) in identifying cancers in patients with fever of unknown origin (FUO). Methods: PCT test and dual-phase $^{18}F$-FDG SPECT were sequentially performed on 50 consecutive patients with FUO. Two radiologists evaluated all $^{18}F$-FDG SPECT data independently. A consensus was reached if any difference of opinions existed. Final diagnosis was based on a comprehensive analysis of results for the PCT test, dual-phase $^{18}F$-FDG SPECT and bacterial cultivation, regarded as a gold standard. Results: Among 50 patients, 34 demonstrated PCT ${geq}0.5{mu}g/L$. Coincidence imaging showed in 37 patients with inflammatory lesions, and 13 with malignancy. Finally, 36 bacterial, 1 fungal and 1 viral infections, as well as 12 cancerous fevers were confirmed by dual-phase $^{18}F$-FDG SPECT with PCT, combined with bacterial cultivation and clinical follow-up. Conclusion: Our study demonstrated that dual-phase $^{18}F$-FDG SPECT in association with PCT could be a valuable tool for diagnosis in tumor patients with FUO.