The viscoelastic properties of a polymeric film, negative photoresist MaN 420, are monitored using a shear horizontal surface acoustic wave (SH-SAW) delay line device throughout the ultra violet (UV) light induced polymer crosslinking process. Viscoelastic constants c44 and eta44 are extracted using the measured S21 transmission response of the device along with the polymer layer thickness, density, and the mechanical properties of the substrate. It is verified that measured phase velocity and attenuation of the surface acoustic wave resulting from the UV exposure of the layering polymer are due to both changes in viscoelasticity and mass of the surface layer. The mass of the polymer film decreases by about 1% due to UV light exposure, whereas the extracted viscoelastic constants of photoresist change on average 2.3% in c44 and 11.8% in eta44.