Inulinases are fructofuranosyl hydrolases that target the β-2，1 linkage of inulin and hydrolyze it into fructose， glucose and inulooligosaccharides (IOS)， the latter are of growing interest as dietary fibers. Inulinases from various microorganisms have been purified， characterized and produced for industrial applications. However， there remains a need for inulinases with increased catalytic activity and better production yields to improve the hydrolysis process and fulfill the growing industrial demands for specific fibers. In this study， we used directed enzyme evolution to increase the yield and activity of an endoinulinase enzyme originated from the filamentous fungus Talaromyces purpureogenus (Penicillium purpureogenum ATCC4713). Our directed evolution approach yielded variants showing up to fivefold improvements in soluble enzyme production compared to the starting point which enabled high-yield production of highly purified recombinant enzyme. The distribution of the enzymatic reaction products demonstrated that after 24 h of incubation， the main product (57%) had a degree of polymerization of 3 (DP3). To the best of our knowledge， this is the first application of directed enzyme evolution to improve inulooligosaccharide production. The approach enabled the screening of large genetic libraries within short time frames and facilitated screening for improved enzymatic activities and properties， such as substrate specificity， product range， thermostability and pH optimum. © 2018 American Institute of Chemical Engineers Biotechnol. Prog.， 34:868-877， 2018.