The purpose of the current experiment was to study the ensiling properties of olive cake with and without added molasses at 2-6% (w/w). The results indicate that molasses enhanced the ensiling fermentation of olive cake, as evidenced from higher lactic acid content and higher lactic acid bacteria numbers at 4% and 6% added molasses. However, when applied at 4% and 6% molasses increased fermentation losses up to 9.4%, probably due to larger yeast population. Polyphenols which could interfere with protein utilization by ruminants, decreased during ensiling by about 40%. It is concluded that molasses added at 3% could improve the ensiling fermentation of olive cake without substantial losses. (C) 2007 Elsevier Ltd. All rights reserved.