Penguasaan perkembangan kognitif anak usia dini diantaranya kemampuan berpikir kritis, akan tetapi tidak semua anak mempunyai kematangan yang sama, sebab dipengaruhi faktor eksternal yaitu lingkungan. Melalui pembelajaran Montessori yang diadakan oleh sekolah Prime Smart Islamic Montessori School menyediakan lingkungan pembelajaran yang sesuai dengan tahap perkembangan anak yaitu kemampuan berpikir kritis. Penelitian bertujuan mengetahui implementasi tujuh balok Montessori yang dapat mengembangkan kemampuan berpikir kritis anak. Penelitian menggunakan metode penelitian studi kasus. Studi kasus adalah penelitian mengenai status subjek penelitian yang berkenaan dengan suatu fase spesifik atau khas dari keseluruhan personalitas. Data penelitian bersumber dari observasi, wawancara, dan dokumentasi dengan subjek penelitian satu tenaga pendidik dan lima anak didik. Dalam menganalisis data, peneliti menggunakan model Miles dan Huberman yaitu reduksi data, penyajian data, penarikan kesimpulan/verifikasi. Tujuh balok Montessori yaitu Knobbed Cylinders, Knobbles Cylinder, Pink Tower, Brown Stairs , Color Box 1 & 2, 2D Geometry Shapes, 3D Geometry dijadikan media belajar yang dapat menstimulasi anak berpendapat, membandingkan konsep besar-kecil, tinggi-rendah, lebar-sempit, banyak-sedikit, menjawab pertanyaan, memecahkan masalah, serta mengaitkan bentuk, warna pada lingkungan sekitar atau pemahamannya. Sehingga, tujuh balok Montessori ini dapat mengembangkan kemampuan berpikir kritis anak usia 4-5 tahun Mastery of early childhood cognitive development includes critical thinking skills, but not all children have the same maturity because it is influenced by external factors, namely the environment. Through Montessori learning held by the Prime Smart Islamic School, the Montessori School provides a learning environment that is appropriate to the child’s developmental stage, namely the ability to think critically. This study aims to determine the implementation of the seven Montessori blocks that can develop children’s critical thinking skills. The research uses case-study research methods. A case study is a study of the status of the research subject concerning a specific or distinctive phase of the whole personality. Research data was sourced from observations, interviews, and documentation with research subjects, including one educator and five students. In analyzing the data, the researcher uses the Miles and Huberman model, namely data reduction, data presentation, and conclusion drawing and verification. Seven Montessori blocks, namely Knobbed Cylinders, Knobbles Cylinder, Pink Tower, Brown Stairs, Color Box 1 and 2, 2D Geometry Shapes, and 3D Geometry Shapes, are used as learning media that can stimulate children to think, compare the concepts of big, small, high, wide, narrow, many, and little, answer questions, solve problems, and relate shapes and colors to the surrounding environment or understanding. Thus, these seven Montessori blocks can develop critical thinking skills for children aged 4–5 years.