This paper presents the first study of phytoliths from the Saharan region. Phytolith analysis shows the potential of reconstructing grassland dynamics during the Holocene, refining our knowledge of palaeoecosystems in the Ubari sand sea, Libya. The lake sediments studied range in age between 3,273–9,440 cal. BP. Tree cover was very low around 3,273–3,436 cal. BP and 6,678–6,796 cal. BP, and the landscape was dominated by C4 grasslands around 6,678–6,796 cal. BP, shifting to a more mixed C3-C4 grassland community around 3,273–3,436 cal. BP. These differences may be caused by the older sample being deposited during the onset of a brief arid period, but a similar phytolith assemblage could arise due to a more pronounced seasonality in the climate, with C3 grasses dominating late and early in the growing season when the climate is cooler and less arid, and C4 grasses becoming dominant in the hot, dry summer season.