Keloid is characterized by excessive scar formation and exuberant collagen synthesis as a result of abnormal wound healing and dermal fibroblastic cell proliferation. Up to date, keloid is still a challenge to clinical therapy because of its high recurrence. In addition, there is no single treatment modality has been proven widely effective. Photodynamic therapy (PDT) is used to treat non-melanoma skin cancer and the mechanisms for PDT are well documented. Traditional PDT employed a combination of 5-aminolevulinic acid (ALA) and red light. However, the effectiveness of PDT in treating keloid remained undetermined. Moreover, the transdermal penetration of the photosensitizer and its activating light source are considered to be limited factors. Therefore, our current study set out to explore the effects of a new developed photosensitizer namely 2-(4-aminophenyl) benzothiazole (H3OMe) plus ultraviolet A (UVA) irradiation on keloid fibroblasts. Dermal fibroblasts from normal healthy donors (FBs) and keloid patients (KFBs) were isolated and cultured with 2 μM and 5 μM H3OMe for 4 hours followed by 0.5 J/cm2 UVA irradiation. Intracellular H3OMe uptake was evaluated by a fluorescence microscope. Cell viability was determined by a cell proliferation assay kit. Intracellular H2O2 production, mitochondrial membrane potential, cell cycle analysis, and active caspase-3 expression were analyzed by flow cytometry. The results showed that intracellular H3OMe accumulation was observed in both FBs and KFBs in a dose-dependent manner. Twenty-four and forty-eight hours after UVA irradiation, cell viability was decreased in FBs and KFBs. The results from cell cycle analysis demonstrated that a significant G0/G1 arrest was observed in KFBs after combinations of H3OMe and UVA treatment. Intracellular H2O2 production after combinations of H3OMe and UVA treatment was higher than UVA irradiation alone in KFBs. In addition, intracellular H2O2 production in KFBs was significantly higher than that of FBs after combinations of H3OMe and UVA treatment. Mitochondrial membrane potential level was decreased in FBs and KFBs after combinations of H3OMe and UVA treatment or UVA irradiation alone. The expressions of active caspase-3 were increased in FBs and KFBs after combinations of H3OMe and UVA treatment. Our current results indicated that combinations of H3OMe and UVA treatment significantly decreased the viability and promoted cell apoptosis in KFBs via enhancing ROS (H2O2) production. However, further studies are necessary to clarify the role of ROS on these phenomena. Taken together, our findings suggested that photodynamic therapy using H3OMe plus UVA irradiation may serve as an adjuvant therapy to reduce the recurrence rate after traditional treatments in keloids.