BACKGROUND: Gut microbiota dysbiosis has been implicated in pulmonary arterial hypertension (PAH). However, the exact roles and underlying mechanisms of multi-kingdom gut microbiota, including bacteria, archaea, and fungi, in PAH remain largely unclear. METHODS: The shotgun metagenomics was used to analyse multi-kingdom gut microbial communities in patients with idiopathic PAH (IPAH) and healthy controls. Furthermore, fecal microbiota transplantation (FMT) was performed to transfer gut microbiota from IPAH patients or monocrotaline (MCT)-PAH rats to normal rats and from normal rats to MCT-PAH rats. FINDINGS: Gut microbiota analysis revealed substantial alterations in the bacterial, archaeal, and fungal communities in patients with IPAH compared with healthy controls. Notably, FMT from IPAH patients or MCT-PAH rats induced PAH phenotypes in recipient rats. More intriguingly, FMT from normal rats to MCT-PAH rats significantly ameliorated PAH symptoms; restored gut bacteria, archaea, and fungi composition; and shifted the plasma metabolite profiles of MCT-PAH rats toward those of normal rats. In parallel, RNA-sequencing analysis demonstrated the expression of genes involved in key signalling pathways related to PAH. A panel of multi-kingdom markers exhibited superior diagnostic accuracy compared with single-kingdom panels for IPAH. INTERPRETATION: Our findings established an association between multi-kingdom gut microbiota dysbiosis and PAH, thereby indicating the therapeutic potential of FMT in PAH. More importantly, apart from gut bacteria, gut archaea and fungi were also significantly associated with PAH pathogenesis, highlighting their indispensable role in PAH. FUNDING: This work was supported by Noncommunicable Chronic Diseases-National Science and Technology Major Projects No. 2024ZD0531200, No. 2024ZD0531201 (Research on Prevention and Treatment of Cancer, Cardiovascular and Cerebrovascular Diseases, Respiratory Diseases, and Metabolic Diseases), the National Natural Science Foundation of China of China (No. 82170302, 82370432), Financial Budgeting Project of Beijing Institute of Respiratory Medicine (Ysbz2025004, Ysbz2025007), National clinical key speciality construction project Cardiovascular Surgery, Reform and Development Program of Beijing Institute of Respiratory Medicine (Ggyfz202417, Ggyfz202501), Clinical Research Incubation Program of Beijing Chaoyang Hospital Affiliated to Capital Medical University (CYFH202209).