The influence of genotype and post-harvest treatments on expansion ability of sour cassava starch wasinvestigated using 13 cassava genotypes from Colombia. Starches from cassava grown at 1000 m and1700 m.a.s.l (3 lowland and 10 highland clones respectively) were modified by fermentation (0 or 30days) and drying (oven or sun) treatments. RVA average peak viscosity decreased regularly from 952 cPin native starch to 699 cP in fermented and sun-dried starch. Granule size analysis revealed that fermen-tation hydrolysed lowland and highland granules by exocorrosion and endocorrosion respectively. Thisresult was corroborated by significantly higher RVA breakdown and lower intrinsic viscosity in highlandclones, reflecting different sensitivity to fermentation. For the first time, amylose contents ranging from15.7 to 21.7% were correlated with expansion ability (3.0-8.6 mL/g) of sour cassava starch. Thereforethe combination of cassava genotypes (mainly amylose content) and post-harvest treatments is key forexpansion ability. Supra-molecular granule structure influenced sensitivity to fermentation.