Juvenile idiopathic arthritis (JIA) is one of the most common autoimmune diseases in children. Our study aimed to evaluate the peripheral blood B and T lymphocyte subpopulations in children with JIA. This case–control study included 20 children with JIA as well as 20 healthy children with matching age and sex as a control group. All patients included in the study were in activity as determined by visual analog scale. In addition to complete clinical evaluation, basic investigations, peripheral blood B and T lymphocyte subpopulations were done to all participants by fow cytometry. JIA patients displayed a signifcant decrease in IgM memory B lymphocytes, switched memory B lymphocytes, and total memory B lymphocytes when compared to the healthy controls. The percentages of naïve B lymphocytes were signifcantly increased in JIA patients than in controls. Total T lymphocytes, CD8+CD28null cells, and CD4+CD28null cells were signifcantly increased in JIA patients as compared to controls. In conclusion; JIA patients have an alteration in both B and T lymphocytes with the predisposition of memory cells which may have a role in sustaining the JIA disease activity.