A large range of equivalent dose (D e ) values was observed by applying the single-aliquot regenerative-dose (SAR) procedure to the optically stimulated luminescence (OSL) signal of single grains of quartz extracted from sediments at the Yujiagou site in the Nihewan Basin, north China. Many quartz grains yielded D e values close to zero, which results in severe age underestimation when compared with the results of potassium-rich feldspar grains measured using post-infrared infrared stimulated luminescence (pIRIR) procedure. Dose recovery tests suggest that the SAR protocol is suitable for D e determination. However, a large grain-to-grain variation in thermal stability was identified based on single-grain pulse-annealing measurements. We found that most of the zero-dose or low-dose grains are associated with thermally unstable OSL signals, which explains the large dispersion of the quartz OSL D e distribution. This is further confirmed by the short lifetime of the unstable OSL signals obtained using single-aliquot pulse-annealing test.