ObjectivesThis study aimed to evaluate oral hygiene behaviour and its determinants among preparatory school students in Gondar city, Northwest Ethiopia.MethodsInstitutional‐based cross‐sectional study was conducted among 423 students to evaluate their oral hygiene behaviour and determinant factors (sociodemographic attributes, oral hygiene knowledge, and attitude to oral hygiene behaviours). Linear regression was employed to identify factors associated with oral hygiene behaviour. A p‐value of <0.05 and a 95% confidence interval were used to declare statistical significance.ResultsA total of 407 students participated with a response rate of 96.2%. The mean age of the participants was 18 (SD ±1.3). The mean oral hygiene behaviour (OHB) score was about 7.89 ± 3.43. Only 9.2%, 21.4%, and 5.7% were brushing their teeth at least twice a day, cleaning their tongue, and flossing at least once a day respectively. Father's educational status (able to read and write (β = 1.99, 95% CI: 0.62, 3.38), completed secondary school (β = 1.68, 95% CI: 0.18, 3.18), and diploma and higher (β = 1.75, 95% CI: 0.33, 3.18)), being from private school (β = 3.25, 95%CI: 2.30, 4.19), knowledge about OHB (β = 0.16, 95% CI: 0.01, 0.30), and attitude towards OHB (β = 0.11, 95% CI: 0.08, 0.14) were significant factors positively associated with better oral hygiene behaviour.ConclusionOral hygiene behaviour was poor among preparatory school students in Gondar city. Father's educational status, students' oral hygiene knowledge, and attitude were found to be significant factors affecting students' oral hygiene behaviour. Thus, tailored school‐based oral health communication programs are highly required to improve students' oral hygiene behaviour.