An attempt has been made to estimate the resident time distribution (RTD) in the KE and EZ elements of the Buss Ko-Kneader. The effects of both rotating and reciprocating motions of the screw were taken in to account in the flow analysis as well as in a simplified mathematical model developed for the RTD estimations. The basic function employed in the present work was F(t) = integral f(t) dt, where f(t) dt defined as dq/q was evaluated as a function of the channel depth. Due to the periodic nature of the system averages of minimum resident time was considered as t,; in the above equation. The computation of the model was carried out to evaluated the F(t) as a function of time for both KE and EZ elements. These results demonstrate that the residence tune distribution in KE element is slightly narrower than that in EZ element.