Objective: To compare the gene expression levels of collagen type I alpha 2 (COL1A2) in children with and without dental fluorosis. Methods: Cross-sectional study involving 92 children between 5 and 12 years of age. Socio-demographic characteristics, the presence of dental fluorosis by means of the Thylstrup-Fejerskov index, and gene expression analysis of COL1A2 in peripheral blood samples by reverse transcription polymerase chain reaction (RT-PCR) assays, were described. For the descriptive analysis, measures of central tendency, dispersion and proportions were used. Differences between the groups (p<0.05) were established by the Student t-test. Results: Mean age was 8.6 (SD=1.9) years, 51.1% were female; 54 children were diagnosed with fluorosis and 38 without fluorosis; prevalence of dental fluorosis was 58.7% (95% CI: 48.4% -68.9%). Gene expression of COL1A2 was statistically significantly lower (p<0.05) in the participants with dental fluorosis. Conclusion: There are differences in the expression levels of the COL1A2 gene among the population under study. Therefore, COL1A2 may be potentially involved in the development of dental fluorosis.