Abstract. Glucomannan is one of the highest viscosity polysaccharides with high water absorbing capacity. This property limits glucomannan applications; hence, it requires modifications. Glucomannan has 5-10% acetyl group which confers its functional properties. Replacing the acetyl with alkali transforms the functional characteristic of modified glucomannan. The aim of this study was to determine the effect of deacetylation conditions on the functional properties of glucomannan of A. oncophyllus. Effects of concentration of Na 2 CO 3 (0.1-0.5 M), reaction time (1-5 h) and temperature deacetylation o C) were studied on glucomannan solubility, viscosity and water binding capacity (WBC). Deacetylation conditions affected solubility, viscosity and WBC of deacetylated glucomannan differently. Concentration of Na 2 CO 3 showed negative impact on solubility, viscosity and WBC of deacetylated glucomannan. Solubility increased with increasing temperature and extending duration of deacetylation. Meanwhile, temperature and reaction time were in a reverse relation with viscosity. These changes of functional properties could be due to removing the acetyl groups and subsequently replacing with the alkali during deacetylation. However, the effect of this replacement to the functional properties of deacetylated glucomannan was not linear with the deacetylation conditions. This could be due to various removal distributions of acetyl groups during glucomannan deacetylation.