Abstract: Objective: To evaluate the level of Ultra-fine Particle (UFP) contamination caused by electrosurgical tools (ESTs) in operating room and explore the influencing factors. Methods: Measurements performed during 98 open surgical operations by ultrafine particle counters. Measurements have been carried out simultaneously at 2 cm, 30 cm and 150 cm away from the source, and also before using and 10 min after stop using ESTs. Results: The densities of UFP before using and 10 min after stop using ESTs were 16.45 μg/m3 and 9.18 μg/m3. The densities of UFP at 2 cm, 30 cm and 150 cm away from the source are respectively 201.73 μg/m3, 115.20 μg/m3, and 25.52 μg/m. The densities of fine particles were 1 289.00 m3, 17 906.00 m3, 8 854.00 m3, 2 896.00 m3 and 929.00 m3 respectively. Patients' BMI, tissue type, vacuum suction, closed operating room were influence factors (P<0.05). Conclusion: electrosurgical smoke is a significant airborne contamination in operating room. Strategies of reducing exposure of surgical staff from electrosurgical smoke should be done to guarantee the surgical staff's physical and mental health.