Recurrent aphthuos ulceration is one of the famous diseases widespread among population. Theorists tried to see the causes and treatment this disease. This book focuses on Bactierological( Types of bactreia in the ulcers), immunological changes (Interleukin-2, Interleukin-10, Human secretory IgA, Tumor Necrosis Factor type ? and CRP Factor) and the biochemical changes (Iron and Zinc levels) of serum and saliva of patients, The study group consisted of 37 patients with recurrent aphthous ulceration, 19 females and 18 males ranged between 13-62 years old. Patients with family history of aphthous ulcer were (23) cases, whereas (14) cases have non. This group selected according to the recommended criteria. While, the control group consisted of 15 subjects ranged between 20-40 years old. This group had no signs of any systemic disease, or any type of aphthous ulceration in the oral cavity. The microbiological results showed that different bacteria were isolated such as viridans Streptococci, Staphylococcus spp, pseudomonas spp, Neisseria spp. and Actinomycetes spp. The serological changes showed high levels of these factors and low level in others in serum of patients.