The ability of an aqueous extract of the sclerotia of Pleurotus tuberregium to modulate hematological parameters was investigated in normal and alloxan treated rabbits.The extract was subjected to atomic absorption spectrophotometric and flame ionization detector-coupled-gas chromatographic (GC-FID) analysis. Diabetes mellitus was induced by a 120 mg/kg body weight intravenous injection of alloxan. Metformin was orally administered at 50 mg/kg, while the extract was administered (both to normal and diabetic rabbits) at 100, 200 and 300 mg/kg.Analysis of the extract showed that it had high contents of calcium, magnesium, manganese and potassium. Eleven known glycosides were detected, comprising mainly of amygdalin (37.7%), digoxin (14.4%), dhurrin (14.0%), linamarin (13.6%), prunasin (10.8%) and digitoxin (8.4%). Also detected were twelve known saponins, consisting mainly of sapogenin (40.3%) and neochlorogenin (21.8%); and twelve known lignans, consisting mainly of matairesinol (59.7%), secoisolariciresinol (20.9%) and lariciresinol (14.9%). Compared to the Diabetic control, the hematocrit, hemoglobin concentration, mean cell hemoglobin, mean cell hemoglobin concentration, mean corpuscular volume, red cell distribution width; and red cell, total white cell, lymphocytes, granulocytes and platelet counts of the treated groups were significantly (p<0.05) higher.The above result showed that the extract had a positive effect on the hemopoietic system of the treated animals, at least at the doses at which it was administered in this study.