This dataset presents sediment load grain size distributions of Bossons stream, one of the subglacial stream draining Bossons glacier meltwater.Bossons glacier is rapidly retreating and its proglacial area is deglaciated for ~30 years. Within this area, Bossons stream flows through an alluvial plain with day-to-day morphological changes. It is an intriguing location to study periglacial and proglacial erosion processes which requires to characterize transported sediments. Since coarse particles are difficult to monitor in such alpine stream environment, this dataset focuses on fine grained particles in suspension load, saltation load 5 cm from bed and bedload.In 2009, a sediment trap constituted by a sole 1.5L-bottle was used to acquire 68 samples. The trap was pickep up every morning (9h00) and evening (20h00) between July 2nd and September 13th 2009.After decantation, drying and weighting, Grain Size Distribution (GSD) of each samples has been determined by laser micro-granulometry. Some sample were analyzed twice to ensure data consistency. Only 12 bedload samples have been analyzed.Saltating particles GSD is unimodal and dominant mode is always greater than 500 µm. Hence, on normal hydrological condition, suspended load, saltating load and bedload correspond respectively to silts, medium to coarse sands and medium to coarse sands together with granular gravels.