Abstract Nama : Munazir Student No. : 1609200080028 Study Program : Magister Degree in English Education Department : English Education Title : An Investigation of The Use of Social Dialect in To Kill a Mockingbird Keywords: Social Dialects, Linguistic Feature, Social Factors, To Kill a Mockingbird. The research aimed at investigating linguistic features and social factors that contribute to social dialects in the conversation of the characters in To Kill a Mockinbird. The source of data in this research is To Kill a Mockingbird novel. The research is concerned on linguistic features (vocabulary, grammar and pronunciation) and social factors (occupation, ethnicity, education and age) of social dialects based on the diversity of the characters’ social background. The collected data were analyzed by using content analysis method which is describing the phenomena based on the sourse of data. While conducting the research, the researcher refers to Holmes (2001) theory in social dialect aspects. The findings show that there are fifty six samples of the conversations and thirteen dominant characters of the investigation. Therefore, it is found that the linguistic features and social factors of social dialect occured from the diversity of social background, such as education, age, ethnicity and occupation.