The understanding and analyzing of solid particle behavior in a liquid is a challenge in numerouse fields and engineering industry as the petroleum or the cosmetic one. It is indeed essential to know the behavior of soft matter process to avoid problems and ensures the product quality. This study presents the viscosimeter development working on a resonant optical signal principle by measuring the Free Spectral Range (FSR) parameter of a resonant optical mode during nanoparticles (NPs) sedimentation in a liquid which consists of a water/glycerol mixture. The photonic structure is composed of racetracks micro-resonators made of a UV210 polymer fabricated by deep-UV photolitography developped on an oxydated silicon layer to get a Si/SiO2 bi-layer. The chip is then integrated in an optical bench to track the evolution of the FSR during the complet sedimentation process. The resonant signal analyse established by an adapted signal processing of silica nanoparticles sedimentation in different water/glycerol concentrations allows us to determine stages and velocity rate of the sedimentation process to finaly access to their viscosity. At the same time, measures are performed on a commercial mechanical rheometer so as to compare the dynamic evolution of their viscosity and their associated FSR. The plot of those data versus the glycerol concentration in water obviously shows a possible mathematical transformation between viscosity and FSR slope. There is therefore a good agreement between mechanical and resonant optical measures ; so this work proves the feasability of an optical viscosimeter based on resonant signal.