One of the difficulties commonly encountered by students in comprehending reading text is lack of vocabulary mastery. Therefore, the researcher in this study decides to organize research that focuses on the effect of vocabulary knowledge toward students reading comprehension ability. The purpose of this study was to investigate whether the students who experience the vocabulary knowledge treatment achieve better than those who do not experience it. The research design of this study was quantitative quasi- experimental study. While, the population of the study was the seven grade students of MTs Miftahul Ulum. From that population, the samples were 43 students of MTs Miftahul Ulum. The instruments of the research were pretest and posttest questions focusing on descriptive text. The questions of the test were made by the researcher. To get valid test, the texts of the test were measured by using readability checker and the test checked deeply by the expert. The scores of the test were collected and analyzed using IBM SPSS version 24. Wilcoxon test and Mann Whitney test were used to analyze the data. The result of the study shows that students’ score of experimental group is significanly higher than students’ score of control group. Therefore, it can be concluded that vocabulary knowledge is a suitable treatment in helping students to improve their reading comprehension. As the suggestion for future researchers, they should add more material for the test, measure the reliability of the test, and conduct vocabulary knowledge treatment toward listening and writing skill. While for the teachers, the English teacher should adopt vocabulary knowledge treatment as their teaching strategies to help them improve their students reading comprehension.