Adjectives had already received special attention in the literature. The existence of an adjective in the formation of a clause and the formation of a sentence is an absolute matter. At least one subject (subject) and verb are required to form a clause or sentence (verb). The phenomenon of using adjective clauses is very common in writing. Writing sequences are the most problematic in learning English because writers should transform the conception of designing various clauses and choosing the appropriate sentence for a written text, and in writing, we are repeatedly acquainted with complex grammar and therefore become skilled in it. The goal of this study is to determine the influence of students' adjectives mastery on their ability in writing descriptive text. This research using a quantitative approach to find out the impact of students' mastery of adjectives on their ability in writing descriptive texts, with correlational analysis Pearson product-moment to analyzing is there any correlation between the students’ mastery of adjective (independent variable) and students’ ability in writing descriptive text (dependent variable) and using simple linear regression to calculate the relationship between the two variables' score. This study uses two tests, test multiple choice for adjective mastery and ability in writing descriptive text. This research implemented 30 samples and was conducted at the tenth grade of MA Mazro'atul Huda Karanganyar Demak in the academic year 2020/2021, it has a population of 90 students. Researchers took 30 students for validity testing and 30 students for reliability testing. Findings show that the quality of students' adjective mastery is sufficient with a score of 0.529, the quality of students' writing ability in the descriptive text is sufficient too with a score of 0.529, In this research, the significant difference is 0.003, which is less than 0.005 and indicates that there is an effect, as well as the outcomes students' adjective mastery, has a 28% influence on students' writing ability in descriptive text, with the remaining 72% coming from another factor. According to these findings, research indicates that mastery of adjectives plays a role in the ability to write descriptive texts, this indicates that the hypothesis has been accepted. The researcher recommends that teachers take an active role in motivating students to achieve their students study adjectives more actively, for students to be able properly and accurately write a variety of English texts