The aim of current trial was to investigate the efficacy of a new plant-specific fungus (Piriformospora indica) rich in mannan as a fungal feed additive in chicks. A control diet was formulated and 5 incremental levels (0.1, 0.2, 0.4, 0.6, and 0.8 g/kg of diet) of P. indica and 750 mg/kg of diet yeast culture or 500 mg/kg L. acidophilus were added to the control diet. Different characteristics and responses were measured during experimental period. P. indica inclusion increased BW and significantly decreased FCR (P ≤ 0.01) but had no effect on feed intake. P. indica significantly enhanced blood glucose level and reduced cholesterol, LDL, total protein, albumin and uric acid concentration of plasma (P ≤ 0.01; P ≤ 0.05). Higher villus height and thinner crypt depth were obtained in chicks fed 0.6 g P. indica in comparison with the chicks fed control diet or diets containing Lactobacillus acidophilus or yeast culture. Protein digestibility was enhanced in chicks fed yeast culture or 0.1, 0.2 and 0.4 g of P. indica (P ≥ 0.001). Gizzard pH was increased and ileal pH was decreased and the relative weight of carcass, bursa of Fabricius and thymus were increased by inclusion of P. indica
