Garden sage (Salvia officinalis) has many therapeut ic properties which one of them is strengthening he matopoiesis. In this study the effects of garden sage’s hydroalc oholic extract on blood parameters in mice were stu died. Fifty female mice were divided in five groups including c ontrol group, placebo group (0.5cc normal saline in jections) and three treatment groups which received 50, 100 and 2 00 mg/kg of hydroalcoholic extract injections in pe ritoneum for twenty days every other day. After twenty days bloo d samples were taken and average hematocrit, red an d white blood cells, MCV, MCH, and MCHC were measured. Resu lts showed that the amount of total white blood cel ls was decreased significantly in all three treatment grou ps in proportion to control group. Red blood cells and averages of hematocrit and hemoglobin were increased significan tly. According to results, the extract of garden sa ge could weaken immune system by decreasing white blood cell s and affected hematopoiesis by increase in red blo od cells.