Dune fields in parts of northern China contain important stratigraphic records of late Quaternary change in the East Asian monsoon. In this study, 33 new optically stimulated luminescence (OSL) ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet-dry climate variation in the Mu Us and Otindag dune fields of north China. The results indicate dune activity and dry climate in the last few hundred years, 14 ka to about 7--8 ka, and 50 ka to 60 ka. The dunes were mainly stable, implying a wetter climate, between about 7--8 ka and 2.4 ka. These results imply a lag of several thousand years between peak summer insolation at 10--11 ka and high summer monsoon rainfall after 7--8 ka. In the investigated regions, the monsoon climate may not respond directly to orbital forcing over millennial time scales. Land surface feedbacks may account for lagged dune field response.