Agro-industrial by-products and crop residues are available in Egypt in large quantities and can play a significant role in the nutrition of ruminants. Using the agricultural by-products in animal nutrition can improve the environmental conditions, economic benefit and the efficiency of agricultural and animal production. The present study was conducted to investigate the effect treatment of date seeds (DS) with preparation of exogenous enzymes (ZADO®) on in vitro gas production (GP) and some ruminal fermentation parameters compared with clover hay (CH). Four doses: 0 (control), 6 (low), 12 (medium) and 24 (high) mg/g dry matter of ZADO® as multi-enzyme additive (ENZ) were added with DS inside the incubation tubes. Clover hay (CH) was used as a positive control. By comparing the untreated DS with CH, the values of cumulative GP, predicted organic matter degradability, and crude protein degradability were significantly (P<0.05) lowered. However, higher levels of ENZ supplementation (24 mg/ g DM) linearly increased GP at 3, 6, 12, 24, 36, and 48 hr., of incubation. The GP kinetics were insignificantly effected by all levels of ENZ. Also, elevating ENZ concentration resulted in a linear increase in the predicted values of short chain fatty acids (SCFA), Metabolizable energy (ME), Net energy of lactation (NEL), and organic matter digestibility (OMD), where the high values of indicated predicted parameters were recorded with the high level of ENZ (24 mg/ g) compared with the untreated DS. ZADO® supplementation lead to a linear increase in degradability of dry matter (DMD), crude protein (CPD) and crude fiber (CFD) with a significant enhancement with using the level of 24 mg/g DM. In conclusion, the obtained results suggested that the dietary addition of preparation enzymes (ZADO®), particularly at level of 24 mg/g DM of DS, has potential effect on improving the efficiency of nutrients digestibility of date seed.