The residence time distribution (RTD) of rice flour during single-screw extrusion cooking at various operating conditions and screw profiles has been measured and a model describing RTD has been developed. Increasing the feed rate caused rite reduction in residence time. High screw speed resulted in short residence rime, but large dispersion number: The non-flight element yielded the longest residence, but smallest dispersion number among three sa ew elements rested. A mathematical model consisting of a plug flow reactor in series with a continuous stirred tank reactor cross-flowing with a dead volume fitted well the experimental data with correlation coefficients (r(2)) higher than 0.988. The analysis showed that P (fraction of plug flow reactor) varied from 0.38 to 0.65. A high screw speed or fitting a mixing disc induced more mixing action and thus a low value of P. The use of the model with literature data demonstrated that the model was applicable to food and non-food single-screw extrusion process. The applications of different models were also discussed.