Food safety control can be realized through contaminant monitoring and regulation in food matrices and food-associated products. Untargeted profiling methods can provide comprehensive results through screening and identification of unexpected compound. In this study, we have successfully employed the untargeted profiling method to screen unexpected compounds, and identified an unexpected contaminant, Irgacure-907, in two of seven commercial cow milk samples. The Irgacure-907 was further confirmed and quantified as 7.9 ± 0.4 ng mL−1 and 21.2 ± 1.9 ng mL−1 through standard addition in two commercial cow milk samples. This is the first study to use untargeted profiling to screen unknown contaminants present in commercial milk. Moreover, the presence of Irgacure-907 in commercial milk has not been reported previously in Taiwan. This untargeted profiling approach can be used to reveal other unknown food contaminants in various food matrices in the future and is beneficial to public health worldwide.