The propagation length of surface plasmon polaritons (SPPs) is investigated experimentally using a 1D metallic grating fabricated on a higher refractive index substrate (Gallium Phosphide, GaP). The experimentally measured value propagation length of the SPP (L-SPP) at 785 nm wavelength is 13.33 +/- 0.13 mu m, which is close to the theoretical value of the L-SPP on an ideal Au-thin film. The SPP resonance observed in far-field measurements confirms the underlying process and the related effects on the L-SPP measured by scanning near field optical microscope (SNOM). Far-field measurements shows that L-SPP is associated with the full width at half maximum (FWHM) of the SPP resonance which in-turn associated with inplane directional scattering of the SPP. (C) 2015 Elsevier B.V. All rights reserved.