Objective: Primary squamous cell carcinoma (SCC) of the ovary in humans is rare. Most cases represent a malignant transformation of ovarian teratoma, Brenner tumor, or endometriosis. The etiology of this cancer remains largely unknown. Human papillomavirus (HPV) infection is a critical factor that induces tumor formation, particularly cervical cancer. Therefore, this study aimed to evaluate the association of HPV with malignant transformation of mature cystic teratoma (MCT) into SCC of the ovary. Materials and methods: The samples included four formalin-fixed paraffin-embedded SCC-MCT tissues and their adjacent tissues from the cervix to the ovaries, 12 cases of benign teratoma ovarian tissues (dermoid tissues), and 11 cases of benign nonteratoma ovarian tissues (nondermoid tissues). The two squamous carcinoma tissues of the cervix were used as control samples. HPV was detected by immunohistochemistry (IHC) with anti-HPV capsid or E6 (HPV type 16/18) antibodies and in situ hybridization (ISH) with three sets of genotyping probes, HPV types 6/11, 16/18, and 31/33. Results: IHC revealed HPV infection associated with the four cases of SCC-MCT and the two cases of control cervical cancer samples. Importantly, HPV was also detected in adjacent reproductive tissues of the SCC-MCT cases, which suggested that the viral particles might spread in an ascending route through the fallopian tubes, endometrium, endocervix, and cervix to the ovaries. ISH revealed HPV type 16/18 in all SCC-MCT cases and HPV type 31/33 in two, with no HPV type 6/11 in any SCC-MCT cases. However, compared with the SCC-MCT cases, the lower detection rates of HPV in dermoid cysts and nondermoid tissues suggested that HPV might not be associated with normal ovarian tissues or benign ovarian teratomas. Conclusion: Our data suggest that high-risk HPV infection might be a causal factor that induces malignant transformation of MCT into SCC of the ovary, although further investigation is still required.