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.During 2010, the sediment trap was constituted by two 1L-bottles kept at 5 cm from bed by a metal rod (following Delft bottle principle). The trap was picked up every evering during spring and two times a day during summer totaling 238 samples.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.