This study aims to determine the relationship between understanding values of the Indonesian Unity precepts and nationalism attitude of class VIII students at SMP Negeri 1 Purbalingga in the even semester of academic year 2020/2021. The method used in this research is a survey research method with a quantitative approach. The population in this study were all students of class VIII at SMP Negeri 1 Purbalingga, totaling 282 students. The sampling technique used in this study is cluster random sampling and the sample used is class VIII E students, totaling 31 students. The data collection technique used in this study is an instrument of multiplechoice test questions and attitude scale statement questionnaires which were analyzed using Pearson Product Moment correlation. The results of data analysis were carried out by comparing r count with r table that is 0.845 > 0.355 which showed a significant relationship between understanding the values of Indonesian Unity precepts and the nationalism attitude of class VIII students at SMP Negeri 1 Purbalingga with a very strong relationship.