The current study was undertaken to evaluate the rumen fermentation characteristics and hematological parameters of yearling calves fed agro- industrial by-products (wheat offal, palm kernel meal and cassava peels) supplemented with Enterolobium cyclocarpum leaves (ECLM) at different inclusion levels. ECLM foliage randomly harvested, sun dried and ground in a mill with 2mm sieve were included in concentrate ration formulated with the agro- industrial by-products at different levels. The experiment was carried out at the Cattle Unit of the Teaching and Research Farm Directorate of Federal University of Agriculture, Abeokuta, Nigeria. Sixteen yearling calves were used for the study in a 90 d experiment. The calves were grouped into 4 and randomly assigned to 4 treatment groups with 0, 5, 10 and 15% ECLM inclusion levels in a completely randomized design with Panicum maximum fed as basal diet. The statistical proceedure used is ANOVA. The ruminal pH, rumen ammonia concentration, total volatile fatty acids, acetic and butyric acids were significantly (P < 0.05) affected by increasing levels of ECLM in the diets. The pH value and NH₃ concentration were highest at 0% ECLM (6.93) and (9.67mg/100mL) respectively and decreased (P < 0.05) with increasing levels of ECLM while the total VFAs increased with increase in ECLM with 10% ECLM having the highest value (129 mmol/100mL) and 0% ECLM having the lowest value (107.67mmol/100mL). ECLM inclusion (P < 0.05) increased the total viable bacteria count with 10% ECLM having the highest value (26.27 × 10⁷) and 0% ECLM having the least value (19.63 × 10⁷). ECLM inclusion increased the bacteria population (P < 0.05), while protozoa population (P < 0.05) decreased and fungal zoospore populations across the treatments were similar. The red blood cells, serum glucose, serum protein and blood urea increased significantly (P < 0.05) with increasing level of ECLM and were highest at 10% but reduced at 15% ECLM inclusion level. In conclusion, Enterolobium cyclocarpum leaves could be used as supplement with other cheap agro-industrial by-products up to 10% level of inclusion in ruminant feeding.