Experiments were conducted to determine the effect of lime pre-treatment on the chemical composition and in vitro rumen degradability of date palm leaves (DPL). Lime pre-treatments, with or without oxygen supply, were applied for 1, 2 and 3 weeks at 25 and 40 °C. Lime was neutralized by the Calcium-Capturing-by-Carbonation process. Delignification and in vitro rumen gas production were significantly influenced by duration, temperature and oxygen. At 40 °C, oxygen presence stimulated more delignification and subsequently increased in vitro rumen degradability. Lime pre-treatment with 0·2 g calcium hydroxide (Ca(OH)2)/g dry biomass for 3 weeks at 40 °C in the presence of oxygen resulted in a 3-fold increase in gas production after 24 h of incubation, compared with untreated biomass. Lime treatment of DPL with aeration resulted in higher lignin removal and subsequent rumen degradability than without aeration. A techno-economic analysis is needed to select the most efficient and economically feasible pre-treatment procedure.