Students’ prior knowledge is a knowledge are owned by student when they get new information or new lesson material in the class at that time and a knowledge that they got in the past time and always memorize it. Students’ prior knowledge could help student to learn one of the English language skills that is writitng ability. Writing ability is one of the productive skill be side speaking ability in learning English language. Writing is related with the text and this research use the descriptive text. Descriptive text is information text about person, animal, thing, or place that could make the reader have visual experience for catching a describe in it. Those variables are chosen by the researcher to find the correlation between them. The goal of this research is to determine whether there is a significant correlation of the following variables : 1) students’ prior knowledge; 2) writing ability. For this study's correlation design, the Pearson Correlation Product Moment quantitative approach was applied. The test results, including multiple choice for students’ prior knowledge and essay writing assessments for writing ability, were used to compile the data. Researcher got 45 students from using simple random sampling method of sample data as many as 153 students. The population of students at the tenth grade in SMAN 4 Kediri are 324 students. According to the results, 17 students in SMAN 4 Kediri's tenth grade have a percentage of 38% "very good" level of prior knowledge, while 14 students in the same class have a percentage of 30% "excellent" level writing skill. There is a substantial association between prior knowledge and writing ability of students in the descriptive text at the tenth grade in SMAN 4 Kediri, according to the results of the correlation of prior knowledge and writing ability of students. It has been established that using SPSS to apply the Pearson Correlation Product Moment method yielded a value correlation (pearson correlation) of “0,609”, or 60,9%, with a significance level of 0 (two-tailed). The correlation result indicates significant at the two-tailed 0.05 or 1% level. It means there is a strong, positive association in this study. The conclusion drawn from this research's alternative hypothesis (Ha) is that there is a substantial correlation between students' prior knowledge and their capacity to write descriptive texts at the tenth grade level in SMAN 4 Kediri.

Key words : Students’ Prior Knowledge, Writing Ability, Descriptive Text