Background. The low self-efficacy of bystander has a great impact on continues bullying action and the low self-efficacy of the bystander as one factor that causes low pro-social behavior of bystander. This present research consists of two studies, which focused on examining self-efficacy training ‘Aku Peduli" in increasing self-efficacy of the bystander and to examine the correlation between self-efficacy and pro-social behavior of bystander.

Methods. Twenty four students of Mts. "X" Sleman which was indicated as the bystander by using peer rating have participated in this research. They consist of twenty-three female and one male. The first study used experimental methods with quasi-experimental pretest-posttest and follow-up design. The effectiveness of the training was evaluated with Skala Efikasi Diri. The data were analyzed by the Wilcoxon Signed-Rank Test. The second study used correlation as a quantitative method. The relationship between the two variables was evaluated with Skala Efikasi Diri and Skala Perilaku Prososial. The data were analyzed by the Spearman Rho Correlation Test.

Result. The result of Wilcoxon Signed-Rank Test showed that there were significant scores at experiment group in the measurement between pretest and follow up, also between posttest and follow up,  with p= 0,001 (p>0,05) and p=0,03 (p<0,05). But, there were not significant scores in the measurement between pretest and posttest with p= 0,085 (p>0,05). The result of Spearman Rho correlation showed that there were a significant correlation between self-efficacy and pro-social behavior of bystander with p=0,008 (p<0,05).

Conclusions. So, the first study conclusion is the training effective for increasing self-efficacy in the respondents for 3-4 weeks after training (follow-up). Then, the second study conclusion is self-efficacy have a positive correlation with the pro-social behavior of bystander. A bystander with higher self-efficacy also had higher pro-social behavior.

Added-Values. The bystander play a significant role by stopping the school bullying, but have been found to be less likely to support victims. When bystander intervenes the bullying, most likely made the bullying stop. In Indonesia, only a few research that make the bystander focus of the reserarch than victims or perpetrators. This training can be an anti-bullying that applied in schools and incrase self-efficacy of bystander.

Keywords: Self-efficacy; bystanders; pro-social behavior