Recurrent aphthous is a painful condition with 10-12% prevalence in the world. Considerable evidence are existed about the relationship between cellular immune response and recurrent aphthous .In this regard, present study carried out to analyze lymphocyte phenotype in patients with aphthous stomatitis in both active and remission phases of the disease . The results showed CD4 T-lymphocytes are decreased during active phase while there were insignificant changes in CD3 and CD8 T-lymphocytes count compared to normal population. CD4/CD8 ratio was also decreased (P≤0.05). CD16 killer lymphocytes and CD19 cells were increased significantly in active phase of the disease (P≤0.05).