The purpose of this study is to investigate the effect of Khan-Academy-assisted grammar teaching on academic success in English lesson. The videos used in the study were downloaded from the Khan Academy (n.d) website. The sample of the study consists of 67 students (34: experiment group, 33: control group) in Sadreddin Konevi Anadolu Imam Hatip High School that is located in Yesilyurt, Malatya, Turkey. Semi-experimental design with control group of pre-test post-test was used. During the experimental procedure, the videos in Khan Academy about present, past and future tense in English were watched by the experiment group. Teaching process of control group was organized in accordance with English Curriculum. "The Achievement Test on Tenses" which was developed by the researchers was used both as the pre-test and the post test. At the end of the study, it was concluded that Khan Academy video-assisted grammar teaching made a significant difference on academic success in English lesson.