It has been focused on the importance of the host inflammatory response in periodontal pathogenesis and progression, treatment has been introduced to control the host response and the method, which diminishes production and activity of MMP by doxycycline, has been used in periodontal field. MMP is a proteolytic enzyme which plays a major role in tissue destruction and MMP-1 is secreted in the periodontally healthy tissue, while MMP-8, 9, 13, etc in the inflammatory state. Among these, MMP-13 has been discovered lately and reported to degrade primarily type II collagen. Periodontal ligament (PDL) cell plays a role in destruction of periodontal tissue. This study was to evaluate the effect of doxycycline and mefenamic acid, non-steroidal antiinflammatory drug on MMP-13 mRNA expression in the rat PDL cell. Doxycycline concentration of $1{sim}100;{mu}g/ml$ was added rat PDL cell and cell activity was measured by MIT assay at day 1 and 3. MMP-13 gene expression was evaluated by RT-PCR after PDL cells were pre-treated for 1hour with doxycycline (50 ${mu}g/ml$) alone or with mefenamic acid ($10^{-6}M$), then added $IL-1{eta}$(1.0 ng/ml) and incubated for 16-18 hours. The results are as follows: 1. Cell activity decreased Significantly at 24 and 72 hours in 100 ${mu}g/ml$ (p<0.05). 2. Level of MMP-13 mRNA was in 20.2% increase by $IL-1{eta}$ and in pre-treating doxycycline group, expression of $IL-1{eta}$ induced MMP-13 mRNA was inhibited by 31% than $IL-1{eta}$ treated only. 3. Mefenamic acid did not inhibit on the expression of $IL-1{eta}$ induced MMP-13 mRNA, while mefenamic acid in combination with doxycycline inhibited the expression by 41% compared to only $IL-1{eta}$ stimulation. These results suggest that doxycycline synergistically inhibit the expression of $IL-1{eta}$ induced MMP-13 mRNA in combination with mefenamic acid.