BACKGROUND:As the bone and marrow tissue have very special structure, it is difficult to simultaneously display the bone with tough hard tissue and bone marrow tissues containing various immature hematopoietic cel s in the conventional process of pathological section preparation. OBJECTIVE:To choose the best decalcifying solution that cannot only completely remove the calcium in the bone tissue but also protect the structure of bone marrow tissues and cel s from damage. METHODS:Bone marrow tissues from the long bone of dogs were randomly divided into four groups. Under the same conditions, the bone marrow tissues were decalcified with 14%formaldehyde saline solution of nitric acid (group A), 14%nitric acid solution (group B), 20%A saline solution of hydrochloric acid formaldehyde (group C) and 20%A hydrochloric acid aqueous solution (group D). Decalcified time was recorded, fol owed by routine dehydration, section, hematoxylin-eosin staining and microscopic observation. Pathological section quality and hematoxylin-eosin staining were compared among the four groups. RESULTS AND CONCLUSION:Group A had the best sections and hematoxylin-eosin staining, strongest decalcified ability, shortest decalcified time and minimum damage to the bone marrow. Group B had the worst results of section and hematoxylin-eosin staining, in which, the bone tissues were loose and became yel ow and the bone marrow tissue were damaged greatly, and the decalcified effect was worse. Group C was worse than group A in decalcified ability, damage degree, section quality and hematoxylin-eosin staining results. Group D also had a better result of section and hematoxylin-eosin staining as wel as exhibited uniform decalcification effect and less damage to the bone marrow, which was ranked between group B and group C. Al the four kinds of decalcifying solutions have a good decalcification ability, but the section quality and hematoxylin-eosin staining results rank as fol ows:Group A>Group C>Group D>Group B. Taken together, 14%formaldehyde saline solution of nitric acid is ideal for the clinical preparation of pathological sections.