Recent animal studies have shown that regulatory T cells play a crucial role in the suppression of the immune response and that depletion of this subset of T cells might lead to development of autoimmune diseases. The aim of this work was to quantify regulatory T cells (CD4+ CD25+) in the peripheral blood of Omani patients with Systemic Lupus Erythematosus (SLE) and Rheumatoid arthritis (RA) and correlate these findings with the disease activity of the patients. Thirty patients with SLE, 30 patients with RA and 25 healthy volunteers were enrolled in this study. Patients were divided into highly active or low active groups, depending on the disease activity. Flow cytometer was used to quantify CD4+ CD25+ T cells in the peripheral blood mononuclear cells (PBMC). We found that both highly active SLE (0.242 ± 0.3) and RA (0.56 ± 0.29) patients had significantly (p<0.001) lower levels of CD4+CD25bright T cells than did normal controls (1.74 ± 0.47%) or patients with low disease activity (SLE=1.54 ± 0.33, RA=1.829 ± 0.76). The decreased number of CD4+CD25bright T cells during disease activity was restored in remitting phase of SLE patients. This data provides further evidence supporting the hypothesis of defect of regulatory T cells in SLE and RA patients; which may have an important implication in the context of the control of the inflammation and development of autoimmunity.