This study aimed to determine the depression, anxiety and stress levels that have negatively impacted nurses' mental health during the COVID-19 pandemic. A sample group of 826 nurses working in Turkey were asked to fill in an online questionnaire in order to evaluate their psychological responses and the related factors that have adversely affected their mental health during the COVID-19 pandemic. In total, 696 nurses (84.3%) showed symptoms of depression, 644 (78%) reported anxiety and 543 (65.74%) reported stress. This study also highlighted that the most concerning factor for the nurses was the risk of transmitting the COVID-19 infection to their household members (89.2%). The most important problems faced by the nurses during COVID-19 included equipment shortages (50.7%), administrative problems (38.5%) and issues such as accommodation and nutrition (27.4%). These were found to have a statistically significant correlation with the nurses' levels of depression, anxiety and stress. The fear of losing a household member, the inability to their household's social needs and the fear of death were among the factors that concerned nurses during the COVID-19 pandemic, significantly affecting their levels of depression, anxiety and stress. Taking the necessary measures to deal with the aforementioned problems and fears is important to protect the health, productivity and efficiency of nurses during the pandemic period.