One main concern related to the performance of unsaturated soils during the construction and service life of earthen structures is loss of matric suction due to the seasonal variations of gravimetric water content (GWC), ground water infiltration and possible development of excess pore water pressure. In addition to reducing the soil shear strength, loss of matric suction as a result of wetting could also reduce the soil-reinforcement interface shear strength in comparison with the as-built value at a lower GWC. This paper presents the results of small-scale pullout and interface tests on a woven geotextile reinforcement material in different marginal soils in order to quantify the difference in the soil-geotextile interface shear strength as a function of GWC for practical applications. A moisture reduction factor [MRF = mu(omega)] is used to account for the reduction in the soil-geotextile interface shear strength as a function of matric suction over a range of GWC values that includes the dry and wet sides of the soil optimum gravimetric water content (GWC(opt)) or optimum moisture content (OMC). It was observed that the interface shear strength of geotextile reinforcement in marginal soils could be significantly lower (e.g. by as much 50%) at only 2% wet of optimum (i.e. OMC+2%) in comparison with OMC-2%, which is assumed to represent the as-built condition.