The purpose of this study is to investigate the effect of mouth wash containing yarrow plant extract on improvement stomatitis due chemotherapy. Double blind clinical trial study is conducted in cancer patients admitted to Shaheed Beheshti Hospital with oral stomatitis and under chemotherapy treatment with an anti-inflammatory drugs. In this study; patient, the nurse examined mouth the patient and give mouthwash solution to the patient were not aware from the content of the solution. Inclusion criteria: informed consent for participation in the study, aged 20 years and older, not receive radiation therapy after diagnosis, not use another mouthwash solution during the study, not receiving systemic antibiotics and antifungals. In this study participants will exclude if they are using irregular (amount, frequency) mouthwash and they cannot tolerate the smell of a solution containing yarrow extract. In this study, 42 patients were selected by convenience sampling with table of random numbers; severity of stomatitis in experimental and control groups is similar. To all patients after admission, are given extract yarrow+ routine solution (glass 1 (experimental)) and the routine solution (lidocaine , dexamethasone, sucralfate, diphenhydramine) (glass 2(control)). Patients 4 times a day, after breakfast, lunch, dinner and before sleeping, first, wash their hands, cleaning teeth with a soft toothbrush and one type of toothpaste, then 15 cc of the solution kept for 3 min in their mouth and then throw away. Patients should not wash their mouth, and refrain from consuming food until one hour after. According to a double blind study, oral mucosa patients on the first, seventh and fourteenth days after getting mouthwash checked by a nurse working in oncology ward who does not know the mouthwash solution and then checklist is completed.