Background :Plaque is a thin layer of microorganism, food leftover and organic material formed on the teeth, and sometimes it is also found in the gum and tongue. The community of complex microbes in the plague is the main cause of toothache such as tooth caries and periodontal disease. Flavonoid content in strawberry has antibacterial activity that can harm the bacterial wall. Plaque control can be done by gargling with strawberry extract (Fragaria x ananassa) as an alternative way to decrease tooth plaque. This research aims at finding the difference before and after gargling with some concentrate of strawberry extract (Fragaria x ananassa) with concentrate of 15%, 45%, and 75% as the most effective to decrease the tooth plaque. Research Objective :The subject of this research belongs to the kind of clinical experimental research with pretest – posttest cross over design within subject. Research Design :The research subjects were the 60 students of the Dentistry Study Program of the Faculty of Medicine and Health Sciences in Universitas Muhammadiyah Yogyakarta. Since the research was within subject, meaning that every subject would get some treatments (5 treatments), the number of sample used was 12 samples. The number of the research subject was chosen from the population got by using purposive sampling method. The data analysis used One Way Anova and extended test using Tukey HSD (Honestly Significant Difference). Result :The normality test result was P > 0.05 showing normal data distribution. From One Way Anova test, the result got was significant value of P = 0.001 (P > 0.05). So, there was a difference in the plaque decrease in every treatment. Tukey HSD test showed that the most effective concentrate in decreasing tooth plague was in the concentrate of 45%. Conclusion :Strawberry extract was effective towards tooth plaque decrease.