Abstract 
This research aimed to determine the effect of assertiveness training to improve assertive behaviour of adolescents passive smoker. This research used repeated treatment design, one group pretest-posttest design. Subjects in this research was 26 adolescents passive smoker of 10th and 11th grade in one of vocational school (SMK) in Kaliwungu. Methods of data collection using the assertive behavior scale of passive smokers and training evaluation sheet. Hypothesis testing was done by using nonparametric statistical analysis, the Wilcoxon signed test. The results of hypothesis test showed Z= -0,470 and significance (p) of = 0.638. It means there is no significant difference between assertive behavior scores on passive smoker before and after given assertiveness training. Conclusion is no significant difference between assertive behavior scores on passive smoker before and after given assertiveness training. Therefore, the research hypothesis not accepted. 
Keywords: assertive behavior, adolescents passive smokers, assertiveness training