Tooth brushing activities have many benefits for dental and oral health. Tooth brushing can clean up food debris and remove dental plaque. The most important time for someone to brush their teeth is before bedtime, because the salivary flow decreases during sleep and the salivary protective effect is reduced. Night becomes the most risky time for dental plaque accumulation, so brushing teeth before bedtime is needed to prevent dental plaque and keep the salivary pH in normal condition. Objective: The purpose of this study was to determine the effect of the habit of tooth brushing before bedtime to plaque index score and salivary pH. Methods: Design of this study was clinical laboratory with post-test only control group design with 15-17 year old students who had fulfilled inclusion criteria, the subjects were divided into two groups, each group consist of 13 person. The first group was instructed to perform a habit of brushing before bedtime for 30 days, while the other group was not instructed to do brushing before bedtime. After 30 days, plaque index scores were measure using the O'leary method and salivary pH measurements using the Mettler Toledo SevenEasy S20 digital pH meter. The result were analyzed using independent t-test statistical tests to compare plaque index score and salivary pH between groups who having a habit of brushing Teeth before bedtime and who do not have a habit of brushing before bedtime. Results: There was a difference in plaque-index score and mean salivary pH between groups who had a habit of brushing before bedtime and who had no habit of brushing their teeth before bedtime. Conclusion: Based on the results of statistical analysis it can be concluded that there is influence of habit of tooth brushing before bedtime to plaque index score and salivary pH