Introduction:
Secondhand smoking is the inhalation of smoke by a nonsmoker. As with most nursing students had been victims of Secondhand smoking Exposure.

Objectives:
The purpose of this study was to investigate factors affecting the avoidance behavior of secondhand smoke among nursing students.

Methods:
The theory of triadic influence was used as a research framework. This study was collect the data via questionnaires from 170 nursing students with multi-stage sampling in Dusit district, Bangkok. Data were analyzed by using descriptive statistics, Pearson correlation and multiple regression analysis.

Results:
The results showed that the majority of samples were female (84.0%), freshman nursing students (22.5%), and secondhand smoke exposure avoidance behavior at a high score (Mean = 3.38). In addition, the multiple regression analysis indicated that intrapersonal influences factors (perceived the benefits of avoiding secondhand smoke, perceived susceptibility of secondhand smoke, and perceived severity of secondhand smoke) (Beta = .187; p =.003), interpersonal social influences factors (smoking control norms, against smoking in society and opinions about the tobacco industry) (Beta = .165; p < 0.05.

Conclusion(s):
The recommendations from this study are the frequency of media information exposure which is the best factor to predict secondhand smoke exposure avoidance behavior of nursing students. Consequently, the future work should develop media information related to secondhand smoke exposure avoidance, such as the benefits of avoiding secondhand smoke, susceptibility of secondhand smoke, severity of secondhand smoke, and also the situation of smoke-free public areas. These will lead to improving secondhand smoke exposure avoidance behavior.