The purpose of this study was to describe the effectiveness of a scientific approach in increasing original thinking ability on buffered solutions topic. This research population was all of students in the 11th grade of MIA at SMA Negeri 1 Bangunrejo for 2014/2015 academic year. This study used quasi experiment method with non equivalent control group design. The 11th grade of MIA2 and MIA3 were used as the sample classes of this research which were obtained by using purposive sampling technique. The result of this research showed that the average n-Gain of original thinking ability in the control class was 0.603 and in the experimental was class was 0.763. Based on t test the average of n-Gain both the research classes were different significantly. It could be concluded that learning by using scientific approach was effective in increasing original thinking ability on buffered solutions topic. Tujuan penelitian ini adalah untuk mendeskripsikan efektivitas pendekatan ilmiah dalam meningkatkan kemampuan berpikir orisinil siswa pada materi larutan penyangga. Populasi penelitian ini yaitu seluruh kelas XI MIA SMA Negeri 1 Bangunrejo tahun pelajaran 2014/2015. Penelitian ini menggunakan metode kuasi eksperimen dengan desain non equivalent control group. Hasil penelitian menunjukkan bahwa nilai rata-rata n-Gain kemampuan berpikir orisinil pada kelas kontrol sebesar 0,603 dan eksperimen sebesar 0,763. Berdasarkan uji t nilai rata-rata n-Gain kedua kelas penelitian berbeda secara signifikan. Berdasarkan hal tersebut dapat disimpulkan bahwa pembelajaran menggunakan pendekatan ilmiah efektif dalam meningkatkan kemampuan berpikir orisinil pada materi larutan penyangga
