This is a randomized, double-blind, controlled, clinical trial which aims to evaluate the effects of green tea mouthwash containing one percent tannin on plaque accumulation, gingivitis, and tooth staining. One tenth percent chlorhexidine mouthwash is used as positive control.40 subjects recruiting from the students of dentistry faculty of Guilan University of Medical Sciences , all of which are systemically healthy , are not under any medication, do not have dental prostheses, and do not wear orthodontic appliances, participate in this study. Upon entry, they sign an informed consent and randomly assign in case and control groups. Plaque and gingival indices as well as gingival bleeding index are recorded at baseline. Scaling and polishing are performed and plaque index score is decreased to zero. During the study period, participants follow their routine oral hygiene methods and are advised not to use any mouthwash other than their respected one. All the participants are provided with a calibrated cup and mouthwashes in dark, coded bottles and are instructed to use 15 ml of the mouthwash twice daily for 1 minute during the 4 weeks of trial. All the indices plus tooth staining index are recorded after 1 and 4 weeks.