The aim of the study was to investigate the effects of different doses of boric acid injected into chicken eggs on bursa of Fabricius and spleen. The study material consisted of three treatment and one control group. On the fourth day of incubation, boric acid dissolved in 0.9% NaCl were injected into eggs at 1.000, 1.500 and 2.000 ppm doses and control group received only 0.9% NaCl injection. Chicks hatched were raised until ten weeks of age (n= 10). Bursa of Fabricius and spleen were evaluated by histological, immunohistochemical and stereological methods. Weight of bursa of Fabricius, relative weight of bursa of Fabricius (P<0.01), volume of bursa of Fabricius, cortical thickness, follicle area and area of follicular medulla significantly reduced (P<0.001) by injection of 1.500 ppm boric acid compared to control group. The number of white blood cells also decreased in 1.000 ppm and 1.500 ppm groups. An increase (P<0.001) was recorded in hemoglobin ratio in 2.000 ppm group when compared with the other treatment groups and control group. There was an increase in 1500 ppm group in terms of spleen weight (P<0.001), relative spleen weight (P<0.01) and plasma cell count (P<0.05) and likewise an increase was noted in 1.000 and 2.000 ppm groups with respect to follicle count and number of apoptotic cells in comparison to control group. In conclusion, low doses of boric acid induced the bursal involution and implicitly increased plasma cell count in the spleen.