Introduction: Rheumatoid arthritis (RA) is a chronic inflammatory peripheral polyarthritis with unclear etiology. RA usually leads to joint deformity and cartilage destruction in joints of RA patients. The aim of this study was to determine the effect of Islamic fasting on RA (rheumatoid arthritis) severity. Methods: A total number of 28 RA patients in an observational study were randomly divided into two groups. The duration of the study was from 2 weeks prior to start of Ramadan month in 2015 until one month after end of Ramadan. One group followed Islamic fasting during the Ramadan month and another group did not fast. The two groups were visited twice: first before Ramadan and the second time after Ramadan. The number of tender and swollen joints, DAS-28 score, patient-VAS, physician-VAS, and ESR and CRP values were recorded. Results: Mean (±SD) number of tender joints decreased from 1.36 (±1.94) to 0.42 (±0.85) in fasting group (P= 0.02). Mean (±SD) number of swollen joints decreased from 0.79 (±1.05) to 0.07 (±0.26) in fasting group (P= 0.02). DAS-28 and physician-VAS also showed significant decrease in fasting group only. Patient-VAS did not show significant decrease in either group. Mean (±SD) DAS-28 score decreased from 2.74 (±1.06) to 2.18 (±0.64) (P= 0.003) in fasting group. In contrast, mean (SD) DAS-28 score decreased from 2.71 (±0.8) to 2.27 (±1.01) (P= 0.24) in non-fasting group. Conclusion: Islamic fasting during the holy month of Ramadan was effective in decreasing RA severity, but further evidence is required to recommend this type of dietary intervention for RA patients.