Abstract: Aqueous solutions of sodium carboxymethyl cellulose (CMC) were used to simulate non-newtonian media. The influence of non-newtonian flow behaviour and draft tube on mass transfer was examined in an annulus air-lift fermentor with 0. 15m in inner diameter and 0. 975m in height, and an empirical correlation was also proposed for the volumetric mass transfer coefficient (KLa). It was also found that as far as highly viscous pseudoplastic fluid is concerned, the introduction of a solid draft tube improves mass transfer and mixing. Therefore,its operational performance is superior to the reactor with window draft tube or without draft tube.