As the periodontal ligament cells show similar phenotype with osteoblasts, periodontal ligament cells are thought to play an important role in alveolar bone remodeling. According to recent studies, receptor activation of nuclear factor $^{kappa}B$ ligand (RANKL) and osteoprotegerin (OPG) are expressed in periodontal ligament cells during tooth movement. Also periodontal ligament cells is known to play an important role in the progression of periodontal disease. This study was designed how the expression of RANKL and OPG in periodontal ligament cells was regulated by IL-1 ${eta}in$ the concentration of $0.01{sim}10$ ng/ml. The results are as follows; 1. Periodontal ligament cells which stimulated by 1L-1 ${eta}$ increased soluble RANKL synthesis by dose-dependent pattern in the concentration of $0.01{sim}10$ ng/ml. 2. 1L-1 ${eta}$ induced mRANKL expression in dose-dependent manner in the concentration of $0.01{sim}5$ ng/ml. 3. mOPG expression was not to be influenced by 1L-1 ${eta}$. These results suggested that rat periodontal ligament cells could regulate osteoclastogenesis by stimulation of production of RANKL.