Introduction: Historically, human infections with clade Ia monkeypox virus (MPXV) primarily occurred through zoonotic transmission with limited secondary human-to-human transmission. Recent studies suggest increasing evidence of human-to-human transmission of some clade Ia lineages. This report documents the first imported clade Ia mpox case in Shanghai, representing the second documented case in China. Methods: Patient demographics, clinical profiles, epidemiological history, and close contacts were obtained through interviews with the patient and attending physicians. Clinical specimens were collected for real-time fluorescent quantitative polymerase chain reaction (qPCR) and whole-genome sequencing. Contact tracing was implemented, involving a 21-day health monitoring of close contacts. Results: The patient presented with moderate symptoms, including fever, rash, and respiratory manifestations. Genome sequencing identified the virus as clade Ia, showing 99.96% nucleotide identity to a strain from the Democratic Republic of Congo (DRC). Eight close contacts were identified with no secondary infection reported. Conclusions: This case was confirmed as an imported clade Ia mpox case originating in the DRC. The “four JOINTs” cross-agency collaborative mechanism between the CDC and customs played a significant role in effectively stopping local transmission. Challenges in remote investigation highlight the need for stronger international collaboration. Establishing an integrated “early warning-control-tracking” system, coupled with public health intervention, is crucial for reducing importation risks and safeguarding national health security.