OBJECTIVES: To evaluate the impact of the workplace smoking ban in South Korea, where the male smoking rate is high (57%), on smoking behavior and secondhand smoke exposure. METHODS: A workplace smoking ban legislation implemented in April 2003 requires offices, meeting rooms, and lobbies located in larger than 3,000 square meter buildings (or 2,000 square meter multipurpose buildings) should be smoke free. A representative cross-sectional survey, the third wave (2005) of health supplements in the National Health Nutrition Survey of South Korea, was used to measure the impact of the 2003 workplace smoking ban implementation on smoking behavior. It contained 3,122 observations of adults 20 to 65 years old (excluding self-employed and non-working populations). A multivariate statistical model was used. The self-reported workplace smoking ban policy (full workplace ban, partial workplace ban, and no workplace ban) was used as the key measure. RESULTS: A full workplace smoking ban reduced the current smoking rate by 6.4 percentage points among all workers and also decreased the average daily consumption among smokers by 3.7 cigarettes relative to no smoking ban. Secondhand smoke showed a dramatic decrease of 86 percent (= -1.74/2.03)from the sample mean for full workplace ban. However, public anti-smoking campaign did not show any significant impact on smoking behavior. CONCLUSIONS: The full workplace ban policy is effective in South Korea. Male group showed bigger impact of smoking ban policy than female group. The public antismoking campaign did not show any effectiveness.