The authors have studied cytomorphologically on the gian cells appearing in the giant cell lesions which had been collected from the biopsies at the department of oral pathology, college of dentistry, Seoul National University. The results are as follows: 1. We can classify two types of giant cells and large sized giant cells which have foamy, large nuclei and prominent nucleoli, and small sized giant cells which have small, round and homogenous stained cytoplasm. 2. We can not see the phagocytosed materials, only can see the foamy microvacuoles in the cytoplasm of giant cells. 3. We can not see the mitotic figures, nore fused figures in giant cells. 4. Osteoclasts in the periphery of bone tissue reveal large and pale stained with H-E stain, giant cells on the granulation tissue and chronic inflammatory tissue reveal deeply stained with hematoxylin and prominent nuclei, but smaller than osteoclasts.