Oral disease is a common public health problem in Bangladesh. Lack of awareness and improper treatment facilities are the main cause of poor oral health condition in our country. This study was conducted to assess the level of knowledge on oral hygiene among the patients attending selected private dental clinics. A descriptive cross-sectional type of study was utilized, among the patients who attended private dental clinics in Chittagong area of Bangladesh. A total of 160 patients were selected purposively and interviewed using a pre-tested semi-structured questionnaire. The mean age of the respondents was 29.20±4.31 years. About 73.1% of the respondents were male and more than half (55.0%) of the respondents had bachelor degree and above, followed by secondary school level of education (19.4%). 73.1% of the participants used to brush their teeth more than twice per day, 55.6% of the respondents used to spent 1-3 minutes while brushing their teeth and the rest spent more than 3 minutes brushing their teeth. The findings revealed that majority of the patients had fair level of knowledge regarding the oral hygiene. The level of knowledge was found to be significantly associated with educational level and monthly income of the respondents.