The risk of surgical site infections (SSIs) is highly associated with the level of microbial contamination settled on a patient's wound. Low or zero microbial contamination could reduce the risk of patients contracting SSIs. To date, the state of microbial contamination in an operating room (OR) for pre- and post-surgery is rarely examined. This exploration is crucial as a patient undergoing surgery tends to contract the SSI if the microbial contamination is high. This study aims to identify the number of microbes present in the OR for pre- and post-surgical procedures. Microbial sampling was performed on 15 ORs in 6 private hospitals located on the western coast of Peninsular Malaysia. Before the microbial sampling, cleanroom performance testing (CPT) was performed to ensure the compliance of operating parameters with the International Organization for Standardization (ISO) Class 7. The CPT was conducted based on ISO 14644-1, Institute of Environmental Science Recommended Practice (IES-RP-CC006.2), and National Environmental Balancing Bureau (NEBB) Procedural Standards for Certified Testing of Cleanrooms. The CPT procedures involved verifying the cleanroom operating parameters: air change rate, differential room pressure, relative humidity (RH), and air temperature. The CPT shows that the air change rate, differential room pressure, RH, and air temperature fell within the recommended operating conditions, ranging from 28/h - 45/h, 6.8 Pa - 22.3 Pa, 51.8 % – 58.9 %, 18.2 °C – 21.6 °C, respectively. The microbes were measured in two phases: pre- and post-surgical procedures. The present study confirms that the microbial contamination for post-surgical procedures increased significantly compared to pre-surgical procedures. The increase in microbial contamination of pre- and post-surgical procedures ranged from 49 to 81 colony-forming units (CFU).