This study was designed to evaluate cytotoxic of 70% ethanolic crude extract of Portulaca oleracea L on normal human lymphocytes (in vitro) In vitro two, parameters were conducted; mitotic index (MI) and blast index (BI) .The cytotoxic effect of plant extract of Portulaca oleracea at (6.4, 3.2, 1.6, 0.8, 0.4 and 0.2 mg/ml) on normal human peripheral lymphocytes in vitro, for 72 hrs was studied. Results indicated a positive relationship between Mitotic index (MI) values and concentration of ethanolic plant extract (0.467±0.03, 0.467±0.09, 0.300±0.06, 0.267±0.07, 0.300±0.07 and 0.267±0.07) respectively, no significant differences noted (P≥0.01) among effects of different concentrations. Mitotic index value of positive control treatment (PHA) (0.700±0.12) differed significantly (P≤0.01) with all concentrations. Blast index (BI) values following treatment with different concentration of ethanolic extract of Portulaca oleracea (6.4, 3.2, 1.6, 0.8, 0.4 and 0.2 mg/ ml) were (4.03±0.37, 3.70±0.17, 3.30±0.61, 3.13±0.24 and 2.77±0.20), without significant differences (P≥0.01).Following treatment with the highest concentration of plant extract (6.4 mg/ml), the BI value was (5.37±0.30) significantly higher (P≤0.01) than those following treatment with other concentrations. Positive control treatment showed highly significant elevation (P≤0.01) in BI (7.67±0.56) compared with all treatments.