The alternate leaves of Oncosiphon piluliferum are fine and delicate, carrot-like or lace-like. They are deeply twice-dissected into narrow lobes. The leaf is about 3 cm long, its lobes about 2 mm wide.

There may be two basal lobes that appear like stipules. The midrib or rachis is usually channelled. The leaves are aromatic, strongly when crushed (Vlok and Schutte-Vlok, 2015; Shearing and Van Heerden, 2008; Van Wyk and Malan, 1997; iNaturalist).