Background: Microorganisms in the mouth are protected from negative environmental conditions by forming biofilms; however, the use of anti-plaque agents in children is not preferred due to toxic side effects. Green tea has been reported to have anti-microbial and anti-dental caries properties. Aims: The aim of this study was to assess the ability of green tea extract to prevent the formation of biofilm on the teeth of children using space maintainers. Methods: Bacteria were isolated from samples obtained from children aged between 8 and 10 years. The micro-titer plate method and Congo red agar were used to assay biofilm formation. Green tea leaves were obtained from Rize, Turkey. Methanol, hexane and distilled water were used for preparing the extracts. The effects of green tea extract and chlorhexidine on biofilm formation were examined using scanning electron microscopy. Results: Presence of S. mutans 3,3, S. anginosus 2.1.b, S. dysgalactie 184.108.40.206, and E. faecium 10.2. was measured in the biofilm samples. The extracts showed a bacteriostatic effect on the test bacteria, and among the green tea extracts, the methanol extract was found to exhibit the highest efficacy against biofilm formation by S. mutans 3.3. Conclusion: Green tea extract showed good efficacy in controlling bacterial growth, and is recommended as a better-tasting alternative for daily oral hygiene due to a lack of known side effects.