An electrochemical sensor is described for the determination of L-dopa (levodopa; 3,4-dihydroxyphenylalanine). An inkjet-printed carbon nanotube (IJPCNT) electrode was modified with manganese dioxide microspheres by drop-casting. They coating was characterized by field emission scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray powder diffraction. The sensor, best operated at a working voltage of 0.3 V, has a linear response in the 0.1 to 10 μM L-dopa concentration range, a 54 nM detection limit, excellent reproducibility, repeatability and selectivity. The amperometric approach was applied to the determination of L-dopa in spiked biological fluids and displayed satisfactory accuracy and precision.