Particle size distributions were measured from till samples collected at seventeen moraines along the Byrd and Nimrod Glaciers. Approximately 2 g of material was separated from till samples, treated with 35% H2O2, and measured 3 – 5 times on a Malvern Mastersizer 2000. All sites are dominated by sand- and gravel-sized material with distinct spatial patterns in the silt and clay content. Till from the north side of Byrd Glacier and along the trunk of Nimrod Glacier have variable modes in the sand fraction and <5% clay. The tills are primarily derived from locally eroded bedrock. Moraines found at the head of both glaciers contain 15% -70% fines (silt plus clay) and are interpreted to contain subglacially-derived sediment. Till deposited in the Ross Sea from outlet glaciers likely contains a mixture basal debris derived from the East Antarctic craton and material eroded as glaciers cross the Transatarctic Mountains.