ObjectiveTo investigate the potential causal relationship between four types of reproductive behaviors and rheumatoid arthritis (RA), with the goal of establishing a theoretical foundation for clinical prevention and treatment strategies. MethodsPooled gene-wide association study (GWAS) data were obtained from large publicly searchable databases. Four characteristics like menarche, menopause, the age of first pregnancy and the age of last pregnancy, which related to reproductive behavior were selected as the exposure factors and RA as the outcome factors. Single nucleotide polymorphisms (SNPs), which were strongly correlated with the phenotype of the exposure factors, were screened as the instrumental variables, and two-sample Mendelian randomization analyses were used to assess the potential causal relationship between the exposure and the disease. Results① The Mendelian randomization analysis utilizing the inverse variance weighted method on two distinct samples revealed a significant negative correlation between the age of first pregnancy and last pregnancy with the risk of RA (OR=0.91, 95%CI 0.85 to 0.98, P=0.011; OR=0.54, 95%CI 0.31 to 0.93, P=0.026). Conversely, no causal relationship was observed between menarche and menopause with RA. Sensitivity analysis confirmed the robustness of the causal relationship, while MR Egger intercept analysis did not identify any potential horizontal pleiotropy (Page of first gestation -RA=0.169, Page of last gestation -RA=0.283). ② Reverse Mendelian randomization analysis revealed a significant positive causal association between RA and the age of first pregnancy, while no causal relationship was observed with the age of last pregnancy (OR=1.07, 95%CI 1.02 to 1.11, P=0.001). ③ Multivariate Mendelian randomization analysis demonstrated that both the age of first pregnancy and last pregnancy in women were inversely associated with the risk of RA (OR=0.88, 95%CI 0.80 to 0.97, P=0.010; OR=0.68, 95%CI 0.48 to 0.97, P=0.033). ④ There existed a negative correlation between the age of pregnancy in women and the risk of developing RA, suggesting a potential protective effect. ConclusionPregnancy age may have a negative causal relationship with the risk of RA, while menarche and menopause have no causal relationship with RA.