Portulaca oleracea is a fleshy annual herb which is distributed throughout temperate and tropical areas of world. The crude extracts of this plant have been reported to have toxic and beneficial effects on hematological functions and blood chemistry in male rats. Air-dried specimen of Portulaca oleracea (3.2 kg) was cold-extracted in methanol for 72 hours. The resulting methanol extract was then subjected to open column chromatography on silica gel for fractionation. Out of the 5 fractions obtained, fraction 4 was then subjected to male rats hematological and plasma biochemical bioassays. Twenty male rats (160 – 180 g) were divided into control (distilled water) and fraction 4 (1, 2, 3, mg/kg) treated groups (5 per group). The animals were orally treated on daily basis for 50 days. Red Blood Cell (RBC) and Total White Blood Cell (TWBC) counts were determined using hemocytometer. Activities of plasma Alanine Amino Transferase (ALT), Aspartate Amino Transferase (AST) and levels of total protein, globulin and albumin were determined by spectrophotometry. Treatment of rats with fraction 4 (2 mg/kg) produced significant (p<0.05) reductions in PCV and lymphocyte value. Fraction 4 (1 mg/kg, 2 mg/kg, 3 mg/kg) caused significant (p<0.05) increases in total protein and albumin levels relative to their respective controls. It can therefore be concluded that fraction 4 of Portulaca oleracea probably has both toxic and beneficial effects on hematological functions and blood chemistry in male rats.