Abstrak. Penelitian ini bertujuan untuk mengetahui pengaruh model pembelajaran problem based oriented project based learning (POPBL) yang diintegrasikan dengan science reflective journal writing (SRJ) terhadap keterampilan berpikir kritis dan keterampilan argumentasi siswa kelas VIII SMP Negeri 8 Bandar Baru. Penelitian ini tergolong jenis penelitian pra-eksperimental dengan desain one group pretest posttest. Populasi pada penelitian adalah seluruh siswa kelas VIII SMP Negeri 8 Bandar Baru yang terdiri atas 1 kelas berjumlah 24 siswa dengan sampel sebanyak 24 responden yang ditentukan melalui teknik purposive sampling. Instrumen penelitian terdiri dari ATP, Modul ajar, lembar kerja peserta didik, lembar observasi keterlaksanaan sintaks, tes keterampilan berpikir kritis, dan tes keterampilan argumentasi. Teknik analisis data menggunakan uji-t berpasangan untuk uji dua sisi. Hasil penelitian menunjukkan terdapat perbedaan signifikan keterampilan berpikir kritis dan keterampilan argumentasi siswa yang diajarkan melalui model POPBL dengan SRJ yang dibuktikan dari nilai signifikansi sebesar 0,000 < 0,05. Abstract. This study aims to determine the effect of problem based oriented project based learning (POPBL) integrated with science reflective journal writing (SRJ) on critical thinking skills and argumentation skills of class VIII students of SMP Negeri 8 Bandar Baru. This research is classified as a type of pre-experimental research with a one group pretest posttest design. The population in this study were all students of class VIII SMP Negeri 8 Bandar Baru consisting of 1 class totaling 24 students with a sample of 24 respondents who were determined through a purposive sampling technique. The research instrument consisted of a syllabus, learning implementation plans, student worksheets, syntax implementation observation sheets, tests of critical thinking skills, and tests of argumentation skills. The data analysis technique uses a paired sample t-test for a two-tailed test. The results showed that there were significant differences in students' critical thinking skills and argumentation skills taught through the POPBL and SRJ models as evidenced by the significance value of 0.000 < 0.05.