The use of agricultural by-products, such as corn cobs, has gained significant attention as a sustainable and promising strategy for developing functional feed additives. This study aimed to produce a functional feed additive enriched with xylo-oligosaccharides (XOS) and yeast protein, using corn cobs as the primary raw material. To efficiently convert the xylan in corn cobs into XOS, a recombinant <i>Saccharomyces boulardii</i> strain displaying endo-xylanase on its cell surface was constructed. Among six anchor proteins evaluated for their efficiency in endo-xylanase expression, the X-Tir1 strain exhibited the highest enzymatic activity. Simultaneous saccharification and fermentation of pretreated corn cobs using the X-Tir1 strain and commercial cellulase were optimized under various pretreatment conditions, resulting in the production of 15.2 g/L of XOS and 12.8 g DCW/L of yeast protein after 72 h of fermentation with corn cobs pretreated using 2% (w/v) NaOH. This study demonstrates an environmentally sustainable and cost-effective approach to upcycling agricultural by-products into value-added functional feed additives, thereby improving feed efficiency in fiber-based diets. Additionally, it underscores the applicability of a cell surface display system as a versatile and effective tool for bioconversion processes.