COVID-19 pandemic has created a lot of work stress, especially among medical professionals, namely among nurses. The absence of the non-invasive stress detecting method using salivary alpha-amylase test in Mongolia served us to perform this study. We consider that the nurse immunization could be managed and boosted if the work stress is detected, and it would serve as the prevention method from the infections in the clinical settings. The study aims to investigate the stress level among medical professionals, particularly the nurses, using a self-report questionnaire, work stress profile, and salivary alpha-amylase during the initial period of the COVID pandemic. In the mid of March 2020, 356 professional medical nurses from three national tertiary centres of Mongolia were involved in this study. We employed a Work Stress Profile (WSP), a self-administered questionnaire that assists the personnel to identify their perceived stressors and assessing the stress at work. As the physical stress marker, we measured the saliva alpha-amylase level in these participants. The vital signs, heart rate, glucose and blood pressure were measured. The correlation method was used. There were 344 females and 12 males. The participants' mean age was 38±9.6 years old. The stress among the medical professionals was high by WSP - it was counted 342 or 96.1% of the personnel suffering from the stress at work: the WSP average was 151.49±26.81. However, age, education and work experience could influence stress at a certain level. The salivary alpha-amylase and WSP scores were correlated directly (p<0.01; r=0.187). The pulse, diastolic blood pressure and salivary alpha-amylase were interrelated. As one of the important personnel at the hospital, nurses are at high risk to get stressed in Mongolia. We concluded that the overloading of work leads to work stress among professional medical nurses, especially during the COVID-19 pandemic.