The impact of starch granule size on 2-octenyl-1-succinic anhydride (OSA) modification remains unclear. To investigate changes of structural, physicochemical, digestibility and emulsifying properties due to OSA modification, five small granule starches (from wheat, rice, oat, quinoa and amaranth) were selected and compared with a standard large granule starch (waxy maize). OSA starches were prepared in 3% (volume by weight) OSA reagent with continuous stirring for 6 h under constant pH of 8.5. The hypothesis was that property changes induced by OSA treatment can be more efficiently achieved in small granule starches (< 10 μm diameter). Small granule OSA starches generally had greater emulsion stability, swelling power and digestibility after gelatinization than waxy maize OSA starch, likely due to the unique physical properties and specific molecular structures of small granule starches, i.e. low sedimentation coefficient, low DP of amylopectin and highly branched amylopectin with short chain length. Granule sizes of OSA starches significantly impact on swelling power, amylose leaching, digestibility and emulsifying capacity, but to different extents depending on botanical origin.