To address exposure to secondhand smoke, which is highly prevalent in Korea, local governments have implemented smoking bans at open public places (parks, bus stops, and school zones) since 2011. Exploiting temporal and spatial variation in the implementation dates of these bans, this study estimates their causal effects on individual smoking behavior. The individual-level longitudinal data from the 2009-2017 Korean Labor and Income Panel Study are linked to the smoking ban legislation information from the National Law Information Center. I find robust evidence that outdoor smoking bans increased the probability of making a quit attempt by 16%. This effect appears immediately after a ban goes into effect and lasts for three or more years. People who spend more time outdoors are more likely to change smoking behavior. I also find heterogeneity in effects across the amount of monetary penalty. Whereas the policy change did not affect the prevalence of smoking overall, higher penalties had stronger impacts on reducing the intensity of smoking and increasing the propensity to try to quit.