Background: To evaluate change in pH in patients undergoing fixed orthodontic treatment. Materials & methods: A total of 20 subjects were enrolled. Patients were diagnosed with class I and class II malocclusion. The pH values were measured with portable pH meter strips at the same four time points. The data were analyzed using SPSS software. Results: A pH value decreased from 7.25 in T1 to 6.84 in T18. This decrease in pH value was statistically significant. Conclusion: There are changes in salivary pH in patients undergoing orthodontic treatment. Keywords: Orthodontics, Salivary pH.