The HB strain of duck Tembusu virus (DTMUV) propagated in the brains of newborn mice was used to prepare antigens for use in the hemagglutination inhibition (HI) test. Results showed that such prepared antigens are highly specific to the serum samples derived from DTMUV-infected animals. No spurious hemagglutination reactions against serum samples specific to avian influenza virus H5, H7, H9 subtypes, Newcastle disease virus, egg drop syndrome virus, duck plague virus, and duck hepatitis A virus were observed. The HI test can detect specific antibodies in the serum samples as early as day 4 after experimental infection of ducks with DTMUV. When compared to a virus neutralization test, the sensitivity is 100%. Overall, the HI test developed is highly specific to DTMUV and can be used in clinical diagnosis of diseases and in vaccine studies to monitor the kinetics of antibody response.