Background Dental caries is a global public health problem, especially for young children. This study aimed to assess the prevalence of dental caries and its associated factors among preschool children in Mizan Aman town, Southwest Ethiopia.Methods A school-based cross-sectional study was conducted from 1 October to 1 December 2022. A total of 354 children and their parents participated using simple random sampling techniques. Data were collected through an oral clinical examination, interviewing the parents and measuring the anthropometry of the children.Results The prevalence of dental caries was 36.4% (95% CI 31.2% to 41.8%). Night feeding (adjusted OR (AOR)=3.98, 95% CI 1.56 to 10.15), children who did not brush their teeth under parental supervision (AOR=2.98, 95% CI 1.60 to 5.57), body mass index (AOR=3.48, 95% CI 1.30 to 9.41) and history of dental visits (AOR=3.05, 95% CI 1.61 to 5.81) were significantly associated with dental caries.Conclusion The prevalence of dental caries in preschool children was found to be high. Children who did not brush their teeth under parental supervision, who had experience of night feeding, who had a high body mass index and who had a history of dental visits were at risk for dental caries. Prevention of those identified modifiable risk factors should be considered to reduce dental caries.