Mental illness is any define disease or condition affecting the brain that influences the way a person thinks, feels, behaves, and relates to others, and to his surroundings Mental disorders are widely recognized as a major contributor to the global burden of disease worldwide. There are limited number of studies on knowledge and attitude towards mental illness among caregivers. Objectives: To assess the knowledge and attitude on existing mental illness among the care givers of mentally ill patient. To find the correlation between the knowledge and attitude on existing mental illness among the caregivers of mentally ill patients. To estimate the associate between knowledge and attitude on existing mental illness with selected demographic variables. Setting: The study will be carried out in the psychiatric OPD at Pondicherry Institute of Medical Sciences. Methods: A Non-experimental descriptive study design was adopted for this study. The study was conducted among the care givers of mentally ill patients at psychiatric OPD at PIMS. 46 care givers were selected by convenience sampling technique. The level of knowledge was assessed by multiple choice questions and level of attitude was assessed by 5 point likert scale on mental illness. Results: Among 46 care givers, adequate level of knowledge on mental illness has been observed 4 (8.7%) among the care givers. Moderate level of knowledge on mental illness has been observed 34 (73.9%) among the care givers. Inadequate level of knowledge on mental illness has been observed 8 (17.4%) among the care givers. Favorable attitude on mental illness has been observed 7 (15.2%) and moderate level of attitude has been observed 39 (84.8%) among the caregivers.