A novel sensor for measuring viscoelastic properties of sodium alginate (SA) in distilled water of concentration (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 w/w%) has been tested. The sensor used is an FBG (Fiber Bragg Grating) fibre optic sensor. It has seen that there is a linear response in terms of area of the peak as the concentration of SA increases and the FWHM increases linearly with a small error bar, indicating the precision of the present sensor. The system proposed will substitute the mechanical Maxwell method for measuring viscoelasticity of polymers, with a mechano-optic sensor.