Introduction: Dental plaque removal is an important goal in oral hygiene program. The public interest in herbal medicine and natural products has grown in the past few years. Siwak (Salvadora persica L. (kharijal)) is an ancient tooth stick that has preventive and therapeutic effects on oral cavity. The aim of the present study is to evaluate the effect of siwak chewing sticks on plaque accumulation on tooth surface. Materials and Methods: In this randomized clinical trial study 80 volunteer was selected randomly for complete the study chart. They were enrolled in the study for being in the one of the four study groups: active siwak, inactive siwak, usual tooth brush and no-oral hygiene. The participants wanted to use their instruction for 6 days. Base line (PI-1) and 3-day (PI-2) and 6-day (PI-3) plaque indexes was recorded by Sillness and Loe method. Data evaluation was done using SPSS-22 and Kruskal Wallis Test, Chi-Square Tests. Results: There was a significant reduction of the plaque index in PI-3 (p= 0.029). But in the others, there was no significant difference in the change of plaque index between groups (p>0.05). Conclusion: It is concluded that siwak were able to reduce dental plaque as a mechanical tooth brush and if it uses in active form (fresh plant), the reduction of plaque accumulation is more prominent and effective.