The research was conducted at the Research Center of Agriculture Faculty of the University of Aleppo. 240 chickens of Babcock B300 strain were used and distributed randomly from day one into four independent groups. Each group included 60 birds distributed into three replicates (20 birds). The control group (A group) was fed a balanced standard feed mixture (1-18 weeks) without additives, while lactic acid bacillus was added to treatments groups according to three levels (50 mg/kg feed; B group, 100 mg/kg feed; C group and 150 mg/kg feed; D group). Haematological analyzes were performed over two- time intervals (1-21 weeks and 22-32 weeks). In the first time interval, results showed that a rise in blood albumin (P<0.001) was also observed in C and D groups compared to the A group. The rates of blood globulin increased (P<0.02) in the D group compared with the rest of the groups. No significant differences were noticed across the various groups for the total number of white blood cells and lymphocytes rates. In the second time interval (productive stage), significant differences (P<0.01) were noticed across the various groups in the percentages of the total protein (the highest value was 4.75 g/dl; B group) and serum albumin (the highest value was 3.26 g/dl; D group). It is concluded from the current study that the addition of probiotics to the mixtures of laying hens had a significant improvement in the immune parameters in the blood.