<p><strong>Abstract: </strong>The purpose of this study is to determine the impact of group investigation learning model with multi representation on the topic of optical devices on scientific reasoning and <em>problem solving</em> skill. This study were carried out using quasi experimental method with pretest-posttest control group design and two XI MIA classes as sample. The result showed that there were an impact of group investigation learning model with multi representation on the topik of optical devices on scientific reasoning and <em>problem solving</em> skill of high school students. The mean value of scientific reasoning and <em>problem solving</em> ability of experimental class students who learned by group investigation learning model with multi representation is higher than control class students who learned by group investigation learning model.</p><strong>Abstrak</strong>: Penelitian ini bertujuan untuk mengetahui pengaruh pembelajaran <em>group investigation </em>dengan multi representasi pada topik alat-alat optik terhadap kemampuan penalaran ilmiah dan kemampuan <em>problem solving</em> siswa SMA. Metode penelitian yang digunakan adalah eksperimen kuasi dengan desain <em>pretest-posttest control group </em>dengan dua kelas XI MIA sebagai sampel. Hasil penelitian menunjukkan adanya pengaruh pembelajaran <em>group investigation </em>dengan multi representasi pada topik alat-alat optik terhadap kemampuan penalaran ilmiah dan pemecahan masalah siswa SMA. Nilai rerata penalaran ilmiah dan kemampuan <em>problem solving</em> siswa kelas eksperimen yang belajar menggunakan pembelajaran <em>group investigation </em>dengan multi representasi lebih tinggi dari siswa kelas kontrol yang belajar menggunakan pembelajaran <em>group investigation</em><em>. </em>