The objective of this study was to analyze the influence of socio-demographic factors on food consumption frequencies among adolescents in Korea. Data were obtained from the Seventh Korea Youth Risk Behavior Web-based Survey (2011 KYRBS), a nationwide representative sample of 75,643 (37,873 males and 37,770 females) middle and high school students. It was carried out as a self-administered on-line survey. The frequency of eating breakfast was 4.8 times per week for middle school students and 4.6 times per week for high school students (p < 0.001). Higher levels of perceived household economic status, family affluence scale (FAS) and education attainment of mother were associated with more frequent breakfast eating. The frequencies of consumption of vegetables and milk were higher in males than in females (p < 0.001). The frequency of consumption fruits was higher in females than in males (p < 0.01). Higher levels of perceived household economic status, FAS and education attainment of mother were associated with more frequent consumption of vegetable, fruits and milk. The frequencies of consumption of soda, fast food and instant noodls were higher in males than in females (p < 0.001). The frequency of consumption of snacks was higher in females than in males. Adolescents with lower levels of FAS and education attainment of mother were at risk for skipping breakfast and consuming of soda, fast food and instant noodls more frequently. Whereas, adolescents with higher levels of FAS, education attainment of mother were more likely to be frequent consumers of vegetable, fruits and milk. These findings demonstrated that being high school students and belonging to lower level of socio-economic status (SES) were associated with undesirable food habits.