This study is aimed at examining (1) the effectiveness of applying the Mistake Buster technique in improving the Senior High School students' English ability to use the Simple Past Tense; (2) to identify the process of English teaching and learning in applying the Mistake Buster technique to improve the English ability of 20 students in a Senior High School to use the Simple Past Tense. This research was an experimental research with the quantitative method. The Mistake Buster technique was the independent variable (x) and the students' English ability in the use of Simple Past Tense was the dependent variable (y). Moreover, the techniques of data collection were the test, questionnaire, and observation. The tests were given twice for the Pre-test and Post-test. The questionnaire was given after the post-test, and observation was conducted while giving the treatment to the class. The results showed that the Mistake Buster technique can improve the students' English ability in the use of Simple Past Tense. It was proven by the improvement of students? mean scores that the score for pre-test was 48 improved to 82 at the post-test score. The low score of the students' pre-test was caused by a lack of knowledge towards the use of positive, negative, and interrogative Simple Past Tense for both nominal and verbal sentences. Moreover, the hypothesis testing by the use of Paired Sample Test revealed that the T-test was 9.292 which was showing the Ha was accepted. Based on the significance score (2 tailed), which was 0.000 proved Ha was accepted. Moreover, the application of the Mistake Buster technique in the learning process is considered to have a positive effect on increasing the ability to understand the Simple Past Tense. Based on the results of observations and questionnaires that 85% of students considered the Mistake Buster technique is a good and very good category.

Mistake Buster Technique

Simple Past Tense

Students’ Ability