Rheumatoid arthritis (RA) is a prevalent autoimmune disease, and there is growing evidence suggesting a potential correlation between dietary factors and the pathogenesis of this condition. In order to investigate the causal relationship between diet and RA, we conducted a two-sample Mendelian randomization (MR) analysis to examine the causal associations between 22 dietary factors and RA. Summary data from genome-wide association studies (GWAS) of RA were obtained from large GWAS meta-analyses. GWAS summary data for 22 dietary factors were obtained from UK Biobank (UKB). Random-effects inverse variance weighted (IVW) was used as the primary method for assessing causality, and analyses of heterogeneity and horizontal pleiotropy were performed to ensure the accuracy of the results. Research indicates a negative genetic causal relationship between cereal intake (OR = 0.64, 95% CI: 0.41 - 0.99, P = 0.048) and oily fish intake (OR = 0.70, 95% CI: 0.52 - 0.95, P = 0.020) with the risk of RA. Other dietary factors were not causally related to RA. Sensitivity analysis shows that our results are reliable. This study provides genetic evidence suggesting that cereal intake and oily fish intake are protective factors for RA, indicating that RA patients and individuals at high risk should make appropriate dietary adjustments.