We report for the low and half elevations of the Arahuay district (Canta, Lima, Perú), a total of 49 species of the family Poaceae, grouped in 28 genera, 14 tribes and four subfamilies. Poa is the most diverse genus with five species, followed by Eragrostis and Nassella with four species each one. The species Calamagrostis spiciformis, Chloris halophila, Lamprothyrsus peruvianus, Festuca glyceriantha, Lolium multiflorum and Poa supina are new reports for the department of Lima. We provide dichotomic keys for genera and species determination. Additional information about habitat, distribution and the studied material is provided for each species.