Objective To conduct an epidemiological investigation on a confirmed case of monkeypox reported in Ju County,Shandong Province,to analyze the reasons for transmission,and to provide reference for the prevention and control of monkeypox. Method According to the Monkeypox Prevention and Control Protocol (2023 Edition),an epidemiological investigation was carried out on a reported monkeypox case in Ju County.Specimens such as one vesicular fluid,one blood sample,and one throat swab from the case,five environmental samples from the case's home,and one throat swab from general contacts were collected.Real-time fluorescence quantitative RT-PCR was used for monkeypox virus nucleic acid detection. Results The suspected monkeypox case A was an HIV-infected man who had engaged in high-risk sexual behavior with another man at a bar.Four days later,he developed symptoms including fever,rash,and vesicles.Case A had eight pocks,and the vesicular fluid tested positive for monkeypox virus nucleic acids.One environmental sample from Case A's home also tested positive for monkeypox virus nucleic acids,and Case A was diagnosed with confirmed monkeypox.Case A had one close contact and one general contact.The close contact could not be traced.The general contact tested negative for monkeypox virus nucleic acids in throat swabs and did not develop symptoms such as fever or rash after home health monitoring,indicating no infection. Conclusion The case was maily infected with monkeypox through sexual transmission.Sexual contact is the main route of transmission for monkeypox.Training for medical personnel should be strengthened to improve their sensitivity in diagnosing monkeypox.