Background:
China took great efforts to protect people from secondhand smoke (SHS), including health education, smoke-free environment creating and smoke-free law promotion. Now, more and more people support smoke-free in public places. This study aims to assess secondhand smoke (SHS) exposure at home and to examine factors associated with it in China.

Methods:
A cross-sectional study was conducted among Chinese aged 15 years and above. Using a multistage complex survey design, 336 counties/districts (PSUs) were selected nationwide. In total, 15,095 individuals completed the survey and the response rate was 92.2%. Data were weighted and analyzed by SPSS 20.0 complex survey data analysis program, and Logistic regression was used for exploring potential factors associated with SHS exposure at home.

Results:
The proportion of nonsmokers exposed to SHS at home was 46.7% (37.4% for male and 51.4% for female). Among female respondents, 41.9% reported being exposed to SHS every day in the last 30 days. SHS exposure rate was highest among primary (50.8%) and middle school (53.4%), followed by high school (46.8%), college and above was the lowest (30.2%). The rate also decreased as respondents' age goes up, nonsmokers in the age group 15-24, 25-44, 45-64, 65 years old and above had 55.8%, 45.5%, 44.0% and 38.8% SHS exposure rate respectively. Moreover, the rate is higher in rural area (57.5%) than in urban area (36.9%). Nonsmoker exposed to SHS at workplace had higher SHS exposure rate at home than those who did not exposed at workplace. (OR=1.40, 95%CI: 1.10 -1.79).

Conclusions:
SHS exposure at home is a serious public health problem, especially for women. Lower education, younger people, and those in rural area are more likely to be exposed to SHS at home. 100% smoke-free policy in workplaces might be helpful to reduce SHS exposure in home.