Pentingnya membangun karakter nasionalis pada era sekaarang sangatlah penting. Upaya tersebut efektif dilaksanakan dalam pembelajaran disekolah dengan dukungan materi ajar yang menarik. Materi IPS khususnya tokoh-tokoh proklamasi merupakan contoh karakter nasionalis yang dapat di tauladani siswa. Pelaksanaan penelitian ini untuk mendeskripsikan: proses pengembangan, kelayakan, kepraktisan, dan keefektifan bahan ajar ensiklopedia berkarakter nasionalisme. Penelitian pengembangan ini menggunakan model 4D (four-D) yang dimodifikasi menggunakan tiga tahapan saja, yaitu: tahap pendefinisian, tahap perancangan, dan tahap pengembangan. Subjek uji coba adalah 19 siswa kelas V SDN Sengguruh. Instrumen pengumpulan data menggunakan angket dan dokumentasi. Hasil penelitian menunjukkan bahwa bahan ajar ensiklopedia layak, praktis dan efektif untuk digunakan. Penilaian oleh ahli media mendapatkan presentase 80%, ahli bahasa mendapatkan presentase 80%, penilaian ahli materi mendapatkan presentase 77,2 %, penilaian praktisi mendapatkan presentase 95,4 %, penilaian siswa mendapatkan presentase 92%, sedangkan untuk keefektifan mendapatkan 78,5%. Berdasarkan paparan hasil penilaian maka bahan ajar ensiklopedia “Layak” dan “Sangat Baik” digunakan di lapangan The importance of building nationalist character in the present era is very important. These efforts are effectively implemented in school learning with the support of interesting teaching material. IPS material, especially the figures of the proclamation, are examples of nationalist characters that can be taught by students. The implementation of this research is to describe: the process of developing, feasibility, practicality, and effectiveness of encyclopedia teaching materials characterized by nationalism. This development research uses a 4D (four-D) model that is modified using only three stages, namely: the stage of defining, designing, and developing. The subjects of the trial were 19 fifth grade students at Sengguruh Elementary School. The instrument of data collection uses questionnaires and documentation. The results showed that encyclopedia teaching materials were feasible, practical and effective to use. Evaluation by media experts gets a percentage of 80%, linguists get 80% percentage, assessment of material experts get a percentage of 77.2%, practitioner assessment gets a percentage of 95.4%, assessment of students get a percentage of 92%, while for effectiveness get 78.5% . Based on the explanation of the results of the assessment, the encyclopedia teaching material "Worthy" and "Very Good" was used in the field