The present invention relates to a pharmaceutical composition containing, as an active ingredient, chemokine-like samdori2 (Sam2) for preventing and treating a mental disease associated with a brain nervous system. By constructing a Sam2-specific knockout zebrafish (wherein, the Sam 2 is expressed in a habenular nucleus) and finding that, through novel tank, scototaxis, and social cohesion tests, the zebrafish shows significantly higher fear and anxiety behaviors than the control； inhibitory neuron expression in neurons overexpressing Sam2 gene is decreased； and a patient due to sam2 gene loss shows autism and the hyperanxiety symptom, the Samdori2 can be usefully applied as an active ingredient for a pharmaceutical composition for preventing and treating a mental disease associated with a brain nervous system.
