Validation of viral safety is essential in ensuring the safety of mammalian cell culture-derived biopharmaceuticals since numerous adventitious viruses get contaminated during the manufacturing process. In particular, Chinese hamster ovary (CHO) cells are highly susceptible to minute virus of mice (MVM), bovine parvovirus (BPV), and bovine herpesvirus (BHV). Therefore, viral detection during CHO cell culturing is necessary to ensure the safety of biopharmaceuticals against viruses. In this study, a multiplex PCR assay was developed and subsequently evaluated for its effectiveness to simultaneously detect MVM, BPV and BHV during the manufacture of cell culture-derived biopharmaceuticals. Specific primers for MVM, BPV, and BHV were selected, and a multiplex PCR was optimized. The sensitivity of the assay was $6.49{ imes}10^1;TCID_{50}/mL$ for MVM, $7.23{ imes}10^2;TCID_{50}/mL$ for BPV, and $5.80{ imes}10^1;TCID_{50}/mL$ for BHV. The multiplex PCR assay was very specific to MVM, BPV, and BHV and was subsequently applied to the validation of CHO cells artificially infected with each virus. It could detect each viral DNA from CHO cells as well as culture supernatants. Therefore, we concluded that the multiplex PCR assay is invaluable for detecting adventitious viruses during the manufacture of cell culture-derived biopharmaceuticals.