Purpose: To evaulate the effects of chlorhexidine and $H_2O_2$ on matrix metalloproteinase-1 (MMP-1), tissue inhibitor of metalloproteinase(TIMP-1, TIMP-2), Type 1 collagen, fibronectin and UNCL expressions in human periodontal ligament fibroblasts (hPDLF). Materials and Methods: $1.2{ imes}10^{-1}%$, $1.2{ imes}10^{-2}%$ and $1.2{ imes}10^{-3}%$ CHX and $3{ imes}10^{-3}%$, $3{ imes}10^{-4}%$ and $3{ imes}10^{-5}%$ $H_2O_2$ and mixture of CHX and $H_2O_2$ were applied to hPDLF for 1 min and 30 min. The mRNA expressions of MMP-1, TIMP-1 and 2, Type 1 collagen, fibronectin and UNCL in hPDLF were analysed by RT-PCR. Results: The result were as follows: 1. The expression of UNCL mRNA was higher than that of other mRNAs. 2. $1.2{ imes}10^{-3}%$ CHX increased mRNA expressions of hPDLF as application time increased. 3. $H_2O_2$ lower than $3{ imes}10^{-3}%$ increased expression of UNCL mRNA, and did not decrease mRNA expression of hPDLF. 4. hPDLF treatment with $1.2{ imes}10^{-1}%$ CHX (with or without $H_2O_2$) resulted in no gene expression. 5. hPDLF treatment with $1.2{ imes}10^{-2}%$ CHX (with or without $H_2O_2$) for 30 minutes resulted in no gene expression. Conclusion: Because low concentration of CHX and $H_2O_2$ increased UNCL mRNA expression of hPDLF, low concentraction of CHX and $H_2O_2$ may have an antioxidative effect.