Tobacco use is a global health problem, including in Taiwan. The present study evaluated the perceived risk of smoking and second-hand smoke among pregnant Taiwanese women using a questionnaire. Seven hundred twenty-four pregnant Taiwanese women were recruited from an online parenting community using convenience sampling in 2013. Pregnant smokers and non-smokers had significantly different perceptions regarding risk of smoking and second-hand smoke during pregnancy. Pregnant non-smokers adopted more behaviors to avoid second-hand smoke both at home and in public than pregnant smokers. We conclude that perceived fetal health risks from smoking and second-hand smoke influenced maternal behavior during pregnancy. Pregnant women's perceptions of the risk of tobacco smoke depended on whether their focus in the decision-making process was on prevention or promotion. Understanding the risk factors associated with smoking and exposure to second-hand smoke during pregnancy may help in developing strategies to reduce such exposure.