Pathophysiology of many psychiatric disorders like major depression involves monoamine transmitters like serotonin & substances that reduces NMDA function,including the magnesium modulated, mono aminergic pathway. Worldwide study showed decreased level of serum serotonin & magnesium in acute depressed patients. This case control,non interventional,institutional study was carried out in Dept. Of Biochemistry of Medical College & Hospital, Kolkata between June 2019 to August 2019, in 50 acute depressed recently diagnosed patients & 50 age and sex matched mentally & physically healthy controls.In the depressed group mean serum serotonin level ( 139 +– 41 ng/ml) was significantly lower than healthy controls ( 230 +– 25 ng/ml). So was the mean serum magnesium level which was also significantly lower in depressed group ( 1.1 +– 0.08 mg/dl) than healthy controls ( 2.1+–0.17 mg/dl). This result was in agreement with most of the researches done worldwide.