Serotonin is a monoamine neurotransmitter produced from tryptophan and abnormal levels of these molecules have been associated with several disorders, notably depression, migraine, bipolar disorder, anxiety and schizophrenia. In the present work, we have developed a novel electrochemical sensor using SnO2-SnS2 nanocomposite for selective and simultaneous determination of depression biomarkers serotonin (SE) and tryptophan (Trp) in the presence of ascorbic acid (AA). The SnO2-SnS2 composite prepared by hydrothermal method was characterized by powder XRD, FE-SEM, FITR, UV–Visible, CV, EIS and SWV techniques. The SnO2-SnS2 modified glassy carbon electrode (SnO2-SnS2/GCE) exhibited two well defined oxidation peaks at 0.43 and 0.83V corresponding to SE and Trp respectively in phosphate buffer saline at pH7. Under optimum conditions, linear relationships between the peak currents and concentrations were obtained in the range of 0.1–700μM for SE and 0.1–800μM for Trp with the lowest detection limits (3s/m) of 45 and 59nM respectively. Significant peak to peak separations and higher peak currents make this electrode suitable for simultaneous detection of the two important neurochemicals SE and Trp. The sensor was successfully applied for the detection of SE in human blood samples and Trp in spirulina with high recovery percentage.