The apparent average molar masses (Mw,app), apparent average radii of gyration (Rg,app), of native sago starch and fractions were determined using asymmetrical flow field‐flow fractionation coupled with multi‐angle light scattering and refractive index detectors (AF4/MALS/RI). Amylose‐type (Fraction A) and amylopectin‐type (Fraction B) were chemically separated from native sago starch. Native sago starch and Fractions (A–B) were dissolved in 1M KSCN using a high pressure microwave vessel. The effect of varying cross flow rates at a fixed channel flow rate upon the Mw,app and Rg,app distributions of native sago starch and Fractions (A–B) were investigated. The average Mw,app values of native sago starch, Fraction (A) and Fraction (B) were 60 × 106, 1.5 × 106 and 60 × 106 g/mol, respectively, with average Rg,app values of 142, 75 and 127 nm, respectively. The sphere‐equivalent hydrodynamic radii (Rh) values for native sago starch and fractions were determined from AF4 experimental parameters.