The objective of this study was to nutrient enriched of cassava starch industry by-product using fermentation method. The experimental design was 2 × 3 factorial in Completely Randomized Design (CRD). The factor A was kind of cassava starch industry by-product (cassava pulp and cassava peel) and combine with factor B (unfermented, naturally fermented and rumen microorganism fermented). The results revealed that the interaction between cassava starch industry by-product and fermentation method were shown in dry matter and crude fiber content. Crude fiber content was decreased (p<0.01) with naturally fermented and rumen microorganism fermented. Crude protein content was increased (p<0.01) with naturally fermented and rumen microorganism fermented. However, rumen microorganism fermented was highest true protein content and lowest NPN content (p<0.01). Nitrogen free extract was reverse affect by crude protein content. Base on this study nutrient enrichment of cassava starch industry by product can do by fermentation method, especially rumen microorganism fermented. The rumen microorganism fermented cassava starch industry by product is potentially useful feed material for mono gastric feeding. © Asian Network for Scientific Information, 2009.