BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a significant global health issue, worsened by pollution and modernisation. Ensifentrine (EFT), a new dual inhibitor of phosphodiesterase PDE3 and PDE4, is being developed for inhalation to target airway inflammation, bronchodilation, and ciliary function in COPD treatment. OBJECTIVE: This study aims to develop and validate a new quantification method for Ensifentrine, as no previous techniques are available, by integrating analytical quality-by-design (AQbD) and green analytical chemistry (GAC) principles. METHODS: An AQbD framework, utilizing Design-expert RESULTS: The statistical analysis confirmed the model's significance and normal distribution. The method, validated according to ICH guidelines, showed good linearity (r GREEN CHEMISTRY ASSESSMENT: The greenness of the developed method was evaluated using tools such as ComplexMoGAPI, AGREE, BAGI, Green certificate-modified Eco-scale, and ChlorTox Scale. Additionally, the EVG method evaluation tool was also used to assess environmental impact, with the results shown in a radar chart. CONCLUSION: This study presents a sensitive and robust RP-UPLC method for quantifying Ensifentrine, combining AQbD and GAC principles. The method, validated according to ICH guidelines, also ensures environmental sustainability. This approach sets a precedent for future analytical method development in pharmaceutical sciences with a focus on sustainability.