Most problems in geotechnical engineering are related to the presence of water in the soil. While the amount of water that a saturated soil can contain is defined by the amount of pores, i.e. soil porosity, soil moisture content under conditions of partial saturation will depend on several factors, such as soil retention characteristics, groundwater depth, hydraulic characteristics of layers and stratification, the amount and type of vegetation as well as the complex interaction that takes place between the surface zone of the soil and the atmosphere. Since changes in moisture content directly affect the effective stresses, strength properties, deformability and permeability of unsaturated soil, the possibility of long- term monitoring of soil moisture is of fundamental importance for various engineering problems and structures, including artificial and natural slopes. Today, moisture content of soil is most often monitored using sensors whose accuracy varies depending on the characteristics of the soil. In this work, the accuracy of the Teros 10 soil moisture sensor was evaluated on a sample of fine quartz sand used in tests on a physical slope model in the Geotechnical laboratory of the Faculty of Civil Engineering in Rijeka. By performing measurements under laboratory conditions on samples with predefined density and moisture content conditions, measurement deviations were identified using the generic factory calibration curve implemented by the equipment manufacturer, especially in the range of nearly-saturated and saturated moisture conditions. To eliminate the deviations and increase the measurement accuracy, a sensor calibration procedure was performed and the obtained calibration curve was used in the interpretation of selected, previously obtained, model test results of slopes exposed to simulated precipitation conditions at 1g load conditions.