Conducting this research aimed at finding out the causes of students‟ errors in using personal pronoun as subject, object, and possessive pronoun. This research was conducted at MTS Al-Hidayah Besusu. It was descriptive research. The population was the seventh grade students consisting of 51 students. The sample was the all students of the seventh grade students. The instruments that the researcher used were questionnaire, test, and interview. Questionnaire and test were the main focuses of the researcher to state the causes of the students errors, while the interview was used to support the questionnaire and test data only. The result of this research was that the students‟ errors were caused by Intralingual Errors, Interlingual Errors, and Developmental Errors. In addition, their errors were caused by Internal Factor and External Factors.