Grasses (Poaceae) are human's most important crop plants and among the most important extant clades of vascular plants. However, the origin and early evolution of grasses is controversial, with estimated ages from molecular dating ranging between 59 - 129 Ma (million years ago). Here we report the discovery of basalmost grasses from the late Early Cretaceous (Albian, 113–101 Ma) of China based on microfossils (silicified epidermal pieces and phytoliths) extracted from a special structure along the dentition of a basal hadrosauroid (duck-billed dinosaur). Thus, this discovery represents the earliest known grass fossils, and is congruent with previous estimations on grass origin and early evolution calibrated by oldest known fossil grasses, highlighting the role of fossils in molecular dating. This discovery also indicates deep diverging grasses probably gained broad distribution across both Laurasian and Gondwanan continents during the Barremian (129 -125 Ma).