A new line of human ovarian serous adenocarcinoma cells, TU-OS-4, was established and characterized. The cells showed a short, spindle-shaped morphology and grew in monolayers without contact inhibition while forming an arrangement resembling a jigsaw puzzle. Chromosome numbers ranged from 55 to 73. The proliferation rate was lower than other serous adenocarcinoma cell lines tested (KF, SHIN-3, and SK-OV-3), and the doubling time was 53.3 h. Western blot analysis showed that TU-OS-4 cells overexpressed epidermal growth factor receptor, human epidermal growth factor receptor (HER) 2, and phosphorylated HER2 protein. The IC(50) values to cisplatin, paclitaxel, and lapatinib were 25.8 μM, 686 nM, and 183 nM, respectively. Heterotransplantation in nude mice reflected the original tumor of the cells. These results suggested that this cell line would be useful to study chemoresistant mechanisms and contribute to establishing novel treatment strategies for patients with ovarian cancer.