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.Grain size analysis of suspended particles requires few grams of material. Ten liter of water were sampled at the same location in Bossons stream on four summer days (July 2nd (n=5), July 16th (n=2), August 2nd (n=1) and August 3th 2010 (n=1)) and one flood event (June 10th 2010 (n=1)).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.uspended particles GSD is bimodal when sand can be transported, unimodal otherwise. The dominant mode is 18 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.