Summary Head and neck cancer is highly invasive. It has a tendency to metastasise to regional or distant sites after incomplete treatment. Photodynamic therapy (PDT) is effective in the treatment of head and neck cancers. To investigate the effect of sublethal PDT on the invasiveness of head and neck cancer cells and to elucidate the possible mechanisms, we initiated this study. Two head and neck cancer cell lines, KJ-1 and Ca9-22, were used in this study. Wound healing assay, migration assay, and matrigel invasion assay were used to evaluate the cell migration and invasion. Immunoblotting was performed to investigate the possibly involved signaling pathways. Sublethal PDT significantly suppressed the migration and invasion of both KJ-1 and Ca9-22 cells. Phosphorylation of the focal adhesion kinase (FAK) and its down-stream Src kinase and extracellular signal-regulated kinase (ERK) were also inhibited after sublethal PDT. Sublethal PDT suppresses the migration and invasion of Ca9-22 and KJ-1 cells. Inhibited phosphorylation of the FAK-Src kinase-ERK signaling pathway may be involved in the PDT-induced migration/invasion suppression.