Background: psychiatric patients often experience levels of loneliness and diminished self-concept. Loneliness among people diagnosed with psychiatric diseases can decrease self-concept; therefore. Aim:  This study aimed to assess the relationship between loneliness and self -concept among psychiatric patients. Subjects and Methods: a descriptive research design was used; the study was conducted at Port-Said Psychiatric Health Hospital. The study involved 214 psychiatric patients from in-patient units and out-patient clinic, the study data were collected by using of the following tools; the Tennessee Self-Concept Scale and University of California, Los Angeles Loneliness Scale. In addition, personal and clinical data questionnaire was added; the data was collected through an interview questionnaire. Results: Study results revealed that, the highest percentage of the studied psychiatric patients had mild loneliness and low self-concept. There was a statistically highly significant difference between loneliness and self-concept among psychiatric patients. Conclusion: There was negative correlation between loneliness and self-concept among psychiatric patients. Recommendations: Psychiatric nurse should educate patient how to alleviate loneliness; also how to perceive strengths for elevation of their self-concept.