In vitro studies were carried out to investigate the effect of using crude glycerol (biodiesel co-product) as a substitute for yellow corn with some feed additives. Corn comprising 30% of the whole diet was substituted by crude glycerol at four levels (0, 25, 50 and 75%) with three types of additives; buffer (NaHCO₃& MgO), dry yeast (Saccharomyces cerevisiea) and fibrolytic enzymes. In vitro dry matter disappearance (IVDMD), organic matter disappearance (IVOMD) and total gas production (GP) were studied. Crude glycerol substitution at 25% significantly increased (P<0.05) IVDMD, IVOMD and GP values, while 50 and 75% glycerol significantly decreased (P<0.05) IVOMD and GP values compared with control. No significant difference was observed for IVDMD value when crude glycerol was included at 50% of yellow corn. Addition of 4 g/kg DM of either fibrolytic enzymes or dry yeast significantly increased (P<0.05) IVDMD by 6.5 and 6%, IVOMD by 6 and 4% and GP by 15.8 and 11.5%, respectively. On the other hand, buffer addition had no effect on measured parameters. Using high level of fibrolytic enzymes or dry yeast (6 g/kg DM) significantly increased (P<0.05) IVDMD, IVOMD and GP values for 25 and 50% glycerol compared with the lower level (4 g/kg DM). In conclusion, crude glycerol in combination either with 6g/kg DM fibrolytic enzyme (ALLZYME^™) or dry yeast (Saccharomyces cerevisiea) could replace up to 50% of the yellow corn equivalent to 15% of the whole dietary DM