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This research is aimed to finding out the effectiveness of the group bibliotherapy in decreasing the aggressiveness of the elementary school students. The research method is experimental research using Pretest-Posttest Control Group Design. The sample was choosen based on the selection using aggressiveness scale. The placement of the experimental group is based on randomization. There were 18 students placed as the experimental group and 18 students placed as the control group. The instrument used for pretest and posttest is aggressiveness scale with 55 questions developed by Setiowati, Suprihatin, and Rohmatun (2017). The bibliotherapy was done in 7 session by using stories which have been rated by the psychologist. The data which analyzed using ANOVA test showed that there were significant differences of the gainscore between the experimental group and the control group with F=3,224, on p=0,0405 (p<0,05), moreover, there were significant differences on the experimental group before and after intervention, t=3,696, p=0,002 (p<0,05), meanwhile, in control group there was no significant difference between pretest and posttest , t=0,401 p=0,693 (p<0,05). Based on the result, it can be concluded that bibliotherapy group is effective to decrease the aggressiveness of the elementary students.