With the increasing prevalence of membranous nephropathy (MN), the gut microbiome (GM) is increasingly implicated in its cause, yet the intricate mechanisms remain unclear. Whether changes in the diversity and richness of gut microbial populations among MN patients contribute to disease prevalence is still unanswered, necessitating further exploration into the potential causative link between the GM and MN.We conducted a comprehensive bidirectional mendelian randomization (MR) study. We selected 211 bacterial taxa using genome-wide association study (GWAS) data provided by the MiBioGen consortium, while GWAS data relevant to MN were obtained from ebi-a-GCST010005. The inverse-variance weighted (IVW) method was the primary technique used to delineate the causal relationship between exposures and outcomes. To confirm the robustness of our results, we used additional methods, including MR-Egger, weighted median, simple mode, and weighted mode. Sensitivity analyses included tests for pleiotropy, heterogeneity, and leave-one-out sensitivity to ensure the integrity of our conclusions. Finally, reverse MR analyses were conducted to assess the likelihood of reverse causality.Using various analytical methods, including the IVW approach, MR-Egger, weighted median, simple mode, and weighted mode, our study identified six microbial taxa with a statistically significant causal link to MN, as indicated by p values <0.05. The implicated taxa are Butyrivibrio (OR = 1.25, 95% CI: 1.001-1.565, p = 0.048), Butyricicoccus (OR = 2.15, 95% CI: 1.005-4.621, p = 0.048), Catenibacterium (OR = 1.49, 95% CI: 1.043-2.134, p = 0.028), Ruminiclostridium 5 (OR = 1.78, 95% CI: 1.140-2.763, p = 0.03), Ruminococcaceae UCG-003 (OR = 1.78, 95% CI: 1.140-2.763, p = 0.011), and Bacillales (OR = 1.52, 95% CI: 1.135-2.025, p = 0.005). Each of these taxa has been established as a risk factor for MN. Notably, Ruminococcaceae UCG-003 and Bacillales were identified as having a bidirectional causal relationship with the disease.Our MR study has revealed a causal link between six microbial taxa and MN, highlighting their potential involvement in the disease's development. These findings represent an initial step into this complex field and underscore the need for more in-depth research.© 2025 S. Karger AG, Basel.