The study was conducted to investigate the effects of eggshell powder on the extrusion behaviour and extrudate properties of rice in a co-rotating twin-screw extruder. A reduction in feed rate was observed with 1% eggshell powder added while feed rate increased as eggshell powder added up to 2% or more. Increase in specific mechanical energy (SME) was proportional to increase in pH with the levels of eggshell powder added being up to 2%. When eggshell powder added more than 2%, no significant change in pH value but decrease in SME were observed. Microstructure of eggshell powder added extruclates showed a fine and friable texture with thinner cell walls and more cell numbers. With increase in levels of eggshell powder could increase L* values but decrease b* values of extrudates. However, no significant change in a* values of extrudates was observed. Adding eggshell powder increased water solubility index (WSI) of extrudates. Increasing the levels of eggshell powder could decrease moisture content (MC) and cross-sectional expansion (CE) but increase longitudinal expansion (LE) of extrudates. The addition of eggshell powder also could increase specific volume (SV) and decrease shear force (SF) of extrudates; moreover, the highest SV and the lowest SF of extrudates were observed as 1% eggshell powder added. (c) 2006 Elsevier Ltd. All rights reserved.