Effects of Boron (B) excess and deficiency on the anatomical structure of Medicago sativa L. have been investigated in hydroponic cultures (-B, Control, +B). According to the findings, it was shown that B deficiency (-B) mostly effected the root cortex parenchyma and then xylem and cambium tissues in the stem. In –B plants, the cambium increased in the stem thickness by dividing irregularly, however the differentiation to xylem decreased. Whereas the differentiation of cambium to xylem did not decrease after 25 ppm B (+B) treatment. There was a significant reduction in all tissues of plants grown in +B as compared to control, and a significant decrease was occurred in the diameter of roots and stems. The cambium tissue in the stem was the least affected one by +B treatment. As the B content in the medium increased, the number of stomata and epidermis cells per surface area (mm2) increased while the size of the cells decreased in the leaves. According to the observations and the data which is obtained by calculating the Degree of Xeromorphy, it is found that M. sativa L. developed xeromorphic structure after +B treatment.