Porphyromonas gingivalis (P.g.), which is a potential pathogen for periodontal diseases, contains lipopolysaccharide (LPS), and this endotoxin stimulates a variety of cellular responses. At present, P.g.-derived LPS-induced cellular responses in human periodontal ligament fibroblasts (PDLFs) are not well characterized. Here, we demonstrate that P.g-derived LPS regulates inflammatory responses, apoptosis and differentiation in PDLFs. Interleukin-6 (IL-6) and -8 (IL-8) were effectively upregulated by treatment of P.g.-derived LPS, and we confirmed apoptosis markers including elevated cytochrome c levels, active caspase-3 and morphological change in the presence of P.g.-derived LPS. Moreover, when PDLFs were cultured with differentiation media, P.g.-derived LPS reduced the expression of differentiation marker genes, as well as reducing alkaline phosphatase (ALP) activity and mineralization. P.g.-derived LPS-mediated these cellular responses were effectively abolished by treatment of mitogen-activated protein kinase (MAPK) inhibitors. Taken together, our results suggest that P.g.-derived LPS regulates several cellular responses via activation of MAPK signaling pathways in PDLFs.