Dental plaque is a thin layer substance that develops naturally on the teeth. Dental plaque is formed by colonizing bacteria such as Streptococcus mutans and Lactobacillus sp that trying to attach themselves to the surface on the tooth, so it can dissolves the enamel and causing caries. Dental plaque can potentially be prevented by mouthwash, which contained antibacterial agents, to inhibit bacteria in the oral cavity. Lime (Citrus aurantifolia) has antibacterial activities against specific bacteria that can cause plaque-forming and caries. The aim of this study was to determine the difference of plaque accumulation before and after gargling using lime (Citrus aurantifolia) juice. This research was conducted by clinical trials. The subjects in this research were 30 students from Nogopuro Elementary School Sleman. Day 1, as control, subjects were gargling used aquadest; and day 2, subjects were gargling used lime (Citrus aurantifolia) juice. Dental plaque scores were measured using PHP-M method, before and after intervention. The result of this study indicated that there was a significantly difference (p<0,05) in PHP-M score before and after gargling using lime (Citrus aurantifolia) juice, whereas PHP-M score after gargling using lime juice was lower than before (using aquadest as control). In conclusion, there was a reduction of plaque accumulation after gargling using lime (Citrus aurantifolia) juice.