The purpose of this study was to investigate subjective symptoms about oral malodor and the knowledge and attitude for bad breath on dental students. The subjects were 213 students from 1st to 6th year undergraduate course of one dental school in Thailand (male: 70, female: 143). Their mean (s.d.) age was 21.0 (1.9). Questionnaire survey was conducted in November 2003. Questionnaire items were subjective symptoms about oral malodor and dry mouth, the knowledge and attitude for bad breath, oral hygiene practice, smoking/drinking habits, and life stress. Five students (2.3%) answered that they concerned their oral malodor often and 87.8% reported sometimes. Of them, 72.9% wanted to receive treatment for their malodor and 70.8% said they suffer from bad breath in daily life. Two‐thirds of students perceived strong oral malodor when waking up. There were no significant differences of the self‐perceived malodor rates between gender or among year of study. More than half of the students did not know that oral diseases and poor oral hygiene are the major causes of bad breath. The students’ attitudes for bad breath were different if the target was family members or friends. The majority of the students (88.7%) answered they perceived dry mouth. Perception of dry mouth was significantly related with self‐reported oral malodor prevalence (P < 0.05). However other oral or behavioral factors did not relate to the self‐reported malodor rates. In this study, dental students perceived bad breath in high prevalence. However the knowledge for bad breath was not enough even the students who already provided dental treatment to the patients. It would be necessary to give them adequate knowledge and methods in education program for managing not only patients’ but also their own oral malodor problem.