Treprostinil is a chemically stable analog of prostacyclin, and inhaled treprostinil was developed to deliver the effects directly to the pulmonary vasculature while minimizing systemic side effects. The objective of the study was to evaluate the efficacy on hemodynamics and exercise capacity, safety, and pharmacokinetics (PK) of inhaled treprostinil in Japanese patients with pulmonary arterial hypertension (PAH). Inhaled treprostinil was administered at three breaths (18 μg)/session four times daily, and the dose was gradually increased to a maximum of nine breaths (54 μg)/session. Endpoints included change in pulmonary vascular resistance index (PVRI) as primary, other efficacy parameters, safety, and PK. Seventeen PAH patients, the majority of whom (76.5%) had been receiving both an endothelin receptor antagonist (ERA) and a phosphodiesterase type-5 (PDE5) inhibitor/soluble guanylate cyclase (sGC) stimulator, received inhaled treprostinil. At Week 12, PVRI statistically decreased by -39.4 ± 25.5% (95% confidence interval: -52.6 to -26.3). The most frequently reported adverse events related to treprostinil were headache, cough, throat irritation, and hot flush. Regarding PK, there were no notable differences in the geometric mean C max and AUC last between Japanese and non-Japanese patients. Treatment with inhaled treprostinil using the dosing regimen approved in the United States resulted in significant improvement in hemodynamics, exercise capacity, and symptoms with a favorable tolerability and safety profile in Japanese patients. Inhaled treprostinil could be a valuable therapeutic option for Japanese patients with PAH, including those receiving a combination therapy with an ERA and a PDE5 inhibitor/sGC stimulator. Trial registration: JAPIC Clinical Trials Information [JapicCTI-194651]., Competing Interests: MK has received grants from Boehringer Ingelheim and Ono Pharmaceutical; royalty from Medical Biological Laboratories; consulting fees from Kissei, Boehringer Ingelheim, and Mochida Pharmaceutical; lecture fees, or speaker fees from Boehringer Ingelheim, Ono Pharmaceutical., AbbVie, Asahi Kasei, Janssen Pharmaceutical, Astellas, Chugai Pharmaceutical, Eisai, Nippon Shinyaku, Mitsubishi‐Tanabe, and Mochida Pharmaceutical; participation on a data safety monitoring board or advisory board at AstraZeneka, Corbus, GlaxoSmithKline, Horizon Therapeutics, and Argenx. KA has received research funds from Mochida Pharmaceutical, Janssen Pharmaceutical, Nippon Shinyaku, Daiichi Sankyo, and Konica Minolta; speaker fees from Mochida Pharmaceutical, Janssen Pharmaceutical, Nippon Shinyaku, Bayer Yakuhin, Daiichi Sankyo, and Otsuka Pharmaceutical; fees for serving on advisory boards from Janssen Pharmaceutical. HK has received speaker fees from Nippon Shinyaku, Janssen Pharmaceutical, Bayer Yakuhin, and Mochida Pharmaceutical; consulting fees from Mochida Pharmaceutical. He belongs to the endowed department by Obama Municipal Hospital. HM has received research funds from Janssen Pharmaceutical, Nippon Shinyaku, and Mochida Pharmaceutical; lecture fees from Janssen Pharmaceutical, Bayer Yakuhin, Nippon Shinyaku, GlaxoSmithKline, and Mochida Pharmaceutical. SM has received research funds from Fukuda Foundation for Medical Technology. TM has received speaker fees from Mochida Pharmaceutical, Janssen Pharmaceutical, and Bayer Yakuhin. SS has received consulting fees from Mochida Pharmaceutical; lecture fees from Nippon Shinyaku, Bayer Yakuhin, Janssen Pharmaceuticals, Bayer AG, Pfizer, and Mochida Pharmaceutical. YS has received speaker fees from Janssen Pharmaceutical, Viatris, Nippon Shinyaku, and Mochida Pharmaceutical. NT has received lecture fees from Janssen Pharmaceutical, Nippon Shinyaku, Mochida Pharmaceutical, Pfizer, and Bayer Yakuhin. IT has received speaker fees from Mochida Pharmaceuticals. He belongs to the endowed department by Nippon Shinyaku, Boehringer Ingelheim, and Mochida Pharmaceutical. KT and SK are employees of Mochida Pharmaceutical. They have received remuneration and travel fees within the framework of their employment. TO has received lecture fees from GlaxoSmithKline, Janssen Pharmaceutical, Nippon Shinyaku, Pfizer, and Bayer Yakuhin; research grants from Pfizer, and Mochida Pharmaceutical; speaker fees from Mochida Pharmaceutical. He belongs to the endowed department of Janssen Pharmaceuticals., (© 2023 The Authors. Pulmonary Circulation published by John Wiley & Sons Ltd on behalf of Pulmonary Vascular Research Institute.)