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Although vaccines are one of the environmentally friendly means to prevent the spread of ticks, there is currently no commercial vaccine effective against <i>Haemaphysalis longicornis</i> ticks. In this study, we identified, characterized, localized, and evaluated the expression patterns, and tested the immunogenic potential of a homologue of <i>Rhipicephalus microplus</i> ATAQ in <i>H. longicornis</i> (HlATAQ). HlATAQ was identified as a 654 amino acid-long protein present throughout the midgut and in Malpighian tubule cells and containing six full and one partial EGF-like domains. <i>HlATAQ</i> was genetically distant (homology < 50%) from previously reported ATAQ proteins and was expressed throughout tick life stages. Its expression steadily increased (<i>p</i> < 0.001) during feeding, reached a peak, and then decreased slightly with engorgement. Silencing of <i>HlATAQ</i> did not result in a phenotype that was significantly different from the control ticks. However, <i>H. longicornis</i> female ticks fed on a rabbit immunized with recombinant HlATAQ showed significantly longer blood-feeding periods, higher body weight at engorgement, higher egg mass, and longer pre-oviposition and egg hatching periods than control ticks. These findings indicate that the ATAQ protein plays a role in the blood-feeding-related physiological processes in the midgut and Malpighian tubules and antibodies directed against it may affect these tissues and disrupt tick engorgement and oviposition.