Approximately 1.29 million COVID-19 cases involving healthcare workers (HCWs) have been reported globally, leading to several hospitals conducting mass testing for early detection of infected HCWs. This study was conducted to report our experience and findings from the mass testing of HCWs from a public hospital in Sabah, Malaysia. The mass testing was conducted from 1st March 2020 to 30th June 2020, and involved self-reported data and laboratory results of 2089 HCWs. All HCWs who took at least two nasopharyngeal swabs for COVID-19 testing at two different time intervals during the study period were included. Throughout the mass testing period, various strategies such as practices of the new norm, daily temperature and symptom checking, wearing of appropriate personal protective equipment (PPE), identification of high-risk areas and travel declaration of staffs were within the hospital for prevention of COVID-19 transmission. We observed a small percentage of COVID-19 infected HCWs (n = 19, 0.91%) from the mass testing. Both symptomatic and asymptomatic COVID-19 HCWs were almost equal in number. A majority of those infected were nurses (n = 16, 0.77%) who had contact exposure to COVID-19 positive person or person under investigation (PUI) (n = 15, 0.72%). Four of the COVID-19 infected HCWs (n = 4/19, 21.05%) had no contact exposure. These HCWs were not identified through contact tracing. Fortunately, they were detected during the mass testing and were isolated promptly. In conclusion, mass testing of HCWs helped in early identification of COVID-19 infected HCWs not identified through contact tracing. Strategies such as stratified mass testing, strict compliance to new norm, appropriate PPE usage and identification of high-risk area were effective in the prevention of COVID-19 infection among HCWs.