This paper was intended for the investigation of control of viscosity in different concentrations and temperatures of nutrient solution for hydroponic system. In this study, we focused on the water structure of the nutrient solution. Viscosity is one parameter in aqueous solutions. The viscosities measured by digital rotary viscometer in different concentrations and in different temperature of nutrient solutions. As a result, the viscosities increased with increasing electric conductivity (EC) of nutrient solution. The viscosity of EC5 (EC 16.31 dS/m) was 1.239 mPa·s at 25 ° C. In different temperature, the viscosity of nutrient solution at 5.5 °C (1.540 mPa·s) was significantly higher than the viscosity at 35 °C (1.136 mPa·s). In conclusion, the result indicate that the liner increase in viscosity with increasing concentration of ions for nutrient solution. Moreover, the viscosities of nutrient solution were correlated with water temperature. These results suggest that the viscosity can be used for control of nutrient solution to cultivate in hydroponic system.