Abstract: To study the specific activity requirement of ¹⁸F-Fallypride for dopamine D₂ receptor PET imaging, ¹⁸F-Fallypride was prepared by nucleophilic reaction and purified by HPLC. The specific activity was measured. Different concentrations of ¹⁹F-Fallypride and ¹⁸F-Fallypride (3.7 MBq) were mixed to simulate the specific activity. After the mixture was intravenous injected into normal mice 10 min, Micro PET was carried out, and then the uptake of ¹⁸F-Fallypride in striatum was analyzed. The striatum uptake of ¹⁸F-Fallypride decreased when the specific activity decreased, and the uptake value with the log concentration of ¹⁹F-Fallypride exhibited S-shaped curve. Based on these, ¹⁸F-Fallypride can be used for striatum Micro PET imaging with the specific activity no less than 1.35 PBq/mol. The specific activity is an important factor in the ¹⁸F-Fallypride dopamine D₂ receptor imaging.