Background: Substance abuse emerges as a significant social issue that negatively affects social functioning, disrupts social harmony. Individuals with low self-esteem have been determined to have a tendency to substance use to control their emotions, behavior and satisfy their need for self-esteem. Aim: To explore the relation between the levels of social functioning and self-esteem among substance abusers at Port-Said Psychiatric Health Hospital. Design: A descriptive correlation research design was utilized in this study. Subjects: were comprised of a sample of 133 substance abusers (males or females). Setting: substance abusers who attended the outpatient unit through the hotline for substance abuse at Port Said Psychiatric Health Hospital. Tools: Two tools were used to collect data in this study; which were Social Functioning Scale (SFS), and Rosenberg Self-Esteem Scale (RSS), in addition to personal and clinical data structured sheet. Results: Three-quarters of the studied substance abusers had a low level of social functioning. About two-thirds of the studied substance abusers had a low level of self-esteem. Conclusion: A statistically significant positive correlation between overall social functioning and total self-esteem among the studied substance abusers. Recommendations: psychosocial intervention should be addressed to substance abusers to improve particular areas of social functioning, such as communication, interpersonal relationships, and employment. Moreover,