Owing to the health benefits offer by low digestible starch, particularly resistant starch (RS), various attempts had been carried out by researchers to reduce the digestibility of starch using a wide arrays of modification methods. In this study, several combinations of acid methanol treatment (AMT) and annealing (ANN) were carried out on sago starch (Metroxylon Sagu) to modify its in vitro digestibility. Sago starch was hydrolysed with 1 and 2 ml of hydrochloric acid (36 %, v/v) at 35oC and 40oC respectively, prior to annealing for 72 hours. The effects of modification on the in vitro digestibility, thermal properties, crystallinity, and morphology were investigated. AMT treatments increased the RS content whilst ANN increased the slowly digestible starch (SDS) fraction (p < 0.05). Two combined treatments induced highest amount of RS (p < 0.05) in sago starch. This RS exhibited better heat stability thus resulted at least three-fold of increment in RS content with significant reduction in glycaemic index after cooking (p < 0.05). Acid hydrolysis enhanced the formation of new crystallites during ANN without changing the crystal pattern of the starch (p > 0.05). Sago starch granules were found agglomerated with minor protuberance, surface erosion and surface fissures after dual-modification.