An amperometric sarcosine biosensor was fabricated based on covalent immobilization of sarcosine oxidase (SarOx) onto the nanocomposite of carboxylated multi -walled carbon nanotubes (cMWCNT)/chitosan (CHIT) and copper nanoparticles (CuNPs), electrodeposited on gold (Au) electrode. The SarOx/CHIT/CuNPs/cMWCNT/Au electrode was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The enzyme electrode exhibited optimum current within 2 s at a potential of 0.2 V against Ag/AgCI, pH 7.0 and 35 degrees C. A linear relationship was obtained between sarcosine concentration in the range, 0.1-100 mu M and current (mA) under optimum conditions. The biosensor exhibited a high sensitivity of 277.5 mu A/mu M/cm(2), a low detection limit of 0.1 pM and excellent storage stability (180 days). The analytical recoveries of added sarcosine in sera at 0.5 mu M and at 1.0 mu M concentration were 95.5% and 97.30 respectively. The precision i.e. within and between-batch coefficients of variation (CVs) were 1.08% and 1.70% respectively. There was a good correlation (R-2 = 0.99) between the level of sarcosine in sera as measured by the standard immuno kit method and the present biosensor. The biosensor measured sarcosine level in sera of prostate cancer patients, which was significantly higher than those of apparently healthy persons (p value < 0.01).