The goal of this research is to know how effective is “Mono-Aksi (Interaction Monopoly)” to increasing Social interaction score of children at Muhammadiyah Tamantirto Kasihan Bantul Elementary school. This research uses Rahmawati‟s (2016) Interaksi Sosial Teman Sebaya quetionnaire as collecting data instrument. This research type is Quasy Experiment with Pre test-Post test design. The population of this research is students at Muhammadiyah Tamantirto Kasihan Bantul Elementary School. The data analyze uses Descriptive Analysis at SPSS program. Based on SPSS analysis the results are as follows: Based on Wilcoxon test: Intervention Class Pretest-Postest Sig. (2-tailed) the result is 0,178 which means unsignificant; Based on Paired Sample T test: Control Class Pretest-Posttest Sig. (2-tailed) the result is 0,063 which means unsignificant; Based on Mann Whitney test: differences between Intervention Class Pretest-Posttest compared with difference between Control Class Pretest-Posttest Asymp. Sig. (2-tailed) the result is 0,551 which means unsignificant. The results of this research show that there aren‟t Mono-aksi (Interaction Monopoly) effectivity for increasing social interaction score in children at Muhammadiyah Tamantirto Kasihan Bantul Elementary School.