Nuclear receptors are critical components of various physiological pathways, significantly influencing insect signal transduction. Although the role of HR78 in tracheal and nervous system development has been well-studied, its function during transformation and reproduction remains underexplored. This study characterizes the nuclear receptor gene AaHR78 in Aedes aegypti, which possesses distinct sequence features, including a DNA-binding domain and a ligand-binding domain. AaHR78 spans 3117 base pairs with an open reading frame (ORF) of 1892 base pairs. Temporal and spatial transcription abundance analysis revealed that AaHR78 is predominantly expressed during the pupal stage, peaking at the white pupal phase. Notable transcription abundance levels were detected in the ovaries, thoraxes, and heads of female mosquitoes. Using RNA interference (RNAi) in Ae. aegypti larvae and adults, we investigated the functional role of AaHR78. Larval interference experiments demonstrated that AaHR78 knockdown disrupted genes associated with the 20-hydroxyecdysone (20E) synthesis and signaling pathways, resulting in elevated 20E levels and accelerated pupation. In adult females, AaHR78 knockdown impaired ovarian development by reducing systemic 20E levels, subsequently decreasing egg production. Furthermore, our results confirm that 20E can directly induce AaHR78 transcription abundance. In conclusion, AaHR78 plays a pivotal role in mediating the effects of 20E on larval development and adult reproduction in Ae. aegypti. These findings provide valuable insights into the AaHR78-20E regulatory network and its potential as a molecular target for mosquito control strategies.