The present study investigated whether parents' antismoking actions mediated the prospective relationship between parental smoking cessation and children's smoking. Smoking status of parents (predictor) was assessed when their children were in 3rd grade, parental antismoking actions (mediators) were assessed when their children were in 11th grade, and children's smoking status (outcome) was assessed when they were in 12th grade. In 20 Washington state school districts, data were collected from 1,600 children (49% female, 91% White) and from their parents. Results showed that children's odds of daily smoking were reduced by 39% (95% CI = 24%-51%) for those whose parents had quit smoking, compared with those whose parents were current smokers. Asking to sit in nonsmoking sections of public establishments was a significant (p<.01) mediator that explained 64% of the association between parental smoking cessation and children's smoking. However, not allowing smoking in the home and asking others not to smoke around them were not significant mediators (p = .10, and p = .06, respectively). In conclusion, asking to sit in a nonsmoking section of a public establishment substantially mediates the relationship between parental smoking cessation and children's smoking.