AIMS To assess the impact of a set of comprehensive tobacco control policies implemented in Taiwan in 2009, including extensive smoke-free policy, advertisement ban, pictorial warning and price increase, on adolescent smoking prevalence. DESIGN Five waves of cross-sectional surveys. SETTING Taiwan, 2004-11. PARTICIPANTS Nationally representative sample of junior high schools aged 13-15 years, in a biennial survey, total sample size 101,100. MEASURES Core questionnaire of the Global Youth Tobacco Survey, including ever smoking, 30-day smoking and number of cigarettes smoked. The magnitude of prevalence change before and after the 2009 policy implementation was quantified by adjusted odds ratios estimated by piecewise logistic regression models. FINDINGS The 30-day smoking prevalence demonstrated an upward trend [odds ratio (OR) = 1.06, 95% confidence interval (CI) = 1.02-1.10] between 2004 and 2008. Significant decline in 30-day smoking prevalence after the 2009 law implementation was observed (OR = 0.84, 95% CI = 0.71-0.99). Those living in non-city areas demonstrated a greater magnitude of change. In addition to changes in prevalence, we observed some delay in the age starting smoking, reduction in smokers who smoke fewer than one cigarette per day, and decrease in smokers who did not buy cigarettes. The decline in smoking prevalence was contributed primarily by the reduction in experimenters. CONCLUSION The comprehensive tobacco control programme introduced in Taiwan in 2009 was associated with a reduction in adolescent smoking, particularly among those in earlier stages of smoking and those who resided in non-city areas.