© 2020 Murakami et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Objective To clarify the relationship between dietary habit and disease activity of rheumatoid arthritis (RA). Methods This study enrolled RA patients who met the ACR/EULAR 2010 classification criteria from Kyoto University Rheumatoid Arthritis Management Alliance (KURAMA) cohort in 2015. 22-item food frequency questionnaire (FFQ) was taken for the measurement of dietary habit in a single-institution cohort of RA (Kyoto University Rheumatoid Arthritis Management Alliance: KURAMA) in 2015. The disease activities of RA using the Disease Activity Score calculated based on the erythrocyte sedimentation rate (DAS28-ESR), Simplified Disease Activity Index (SDAI), Health Assessment Questionnaire (HAQ), and serum matrix metalloproteinase-3 (MMP-3) level, the use of disease-modifying anti-rheumatic drugs (DMARDs), disease duration, rheumatoid factor, anti-cyclic citrullinated antibody, and body mass index were also examined. All of them were combined and statistically analyzed. Results 441 RA patients (81% women; mean age 65 years; mean disease duration 15 years) were enrolled from the KURAMA cohort. Average Disease Activity Score-28 using the erythrocyte sedimentation rate (DAS28-ESR) was 2.7. Univariate analysis showed that intake frequency of vegetables had a statistically significant negative correlation with disease activity markers, such as DAS28-ESR (ρ = -0.11, p<0.01), Simplified Disease Activity Index (SDAI) (ρ = -0.16, p<0.001), matrix metalloproteinase-3 (MMP-3) (ρ = -0.21, p<0.0001), and Health Assessment Questionnaire (HAQ) (ρ = -0.13, p<0.01). Factor analysis with varimax rotation was done to simplify the relevance of disease activity to various food items. 22 foods were categorized into five dietary patterns: "seafoods", "vegetables/fruits", "meats/fried foods", "snacks", and "processed foods". The multivariate analysis adjusted for clinically significant confounders showed that "seafoods" had statistically significant negative correlations with DAS28-ESR (β = -0.15, p<0.01), SDAI (β = -0.18, p<0.001), MMP-3 (β = -0.15, p<0.01), and HAQ (β = -0.24, p<0.0001). "Vegetables/fruits" had statistically significant negative correlations with SDAI (β = -0.11 p<0.05), MMP-3 (β = -0.12, p<0.01), and HAQ (β = -0.11, p<0.05) Conclusions These results suggest that high intake frequency of vegetables/fruits and/or seafoods might correlate with low disease activity.