This study aims to determine the effect of guided inquiry learning models aided with learning journal on activities and cognitive learning outcomes students of class X SMAN 2 Tulang Bawang Tengah in "Ecosystem" materials. The study samples were 64 students of class X that were selected bytotal sampling technique. The research instrument used pretest-posttest question and observation sheet of student learning activities. The design used was nonequivalent pretest-posttest control group design. Data onactivities were analyzed descriptively, while pretest-posttest and n-Gain values were analyzed by Independent Sample t-test. The results of the study showed that the average percentage activity was 76.2 with good criteria with N-Gain average that was 0.59 with medium criteria. Thus the application of the guided inquiry learning model aided with learning journal has a significant effect on the activities and cognitive learning outcomes of students in "Ecosystem” materials. Penelitian ini bertujuan mengetahui pengaruh model inkuiri terbimbing berbantu jurnal belajar terhadap aktivitas dan hasil belajar kognitif peserta didik kelas X SMA Negeri 2 Tulang Bawang Tengah pada materi“Ekosistem”. Sampel penelitian adalah 64peserta didik kelas X dipilih melalui teknik total sampling. Instrumen penelitian menggunakan soal pretest-posttest dan lembar observasi aktivitas belajar peserta didik. Desain yang digunakan yaitu non-equivalent pretest-posttest control group design. Data aktivitas dianalisis secara deskriptif, sedangkan nilai pretest-posttest dan n-Gain dianalisis dengan uji Independent Sample t-test. Hasil penelitian menunjukkan persentase rata-rata aktivitas keseluruhan sebesar 76,2 termasuk kriteria baik dengan rata-rata n-Gain sebesar 0,59 termasuk kriteria sedang. Dengan demikian penerapan model inkuiri terbimbing berbantu jurnal belajar berpengaruh terhadap aktivitas belajar peserta didik dan berpengaruh signifikan terhadap hasil belajar kognitif peserta didik pada materi “Ekosistem”.Kata kunci: aktivitas belajar, ekosistem, hasil belajar kognitif, inkuiri terbimbing, jurnal belajar