Mental well-being is a key for successful and productive living of each individual. An imbalance can occur due to various stressors and environmental factors. Due to academic pressures, distance from home and financial burden, nursing students often meet with mental health problems. The objective of this study was to determine the mental well-being of nursing students in Slovenia and Northern Ireland, and to compare the results obtained. A descriptive cross-sectional study design was used. The survey was carried out in 2017 among nursing students in Slovenia and Northern Ireland using the Warwick-Edinburgh Mental Wellbeing Scale. The study included 90 students from Slovenia and 109 from Northern Ireland. Nursing students in both countries reported average level of mental well-being. Nursing students in Slovenia have significantly higher (p < 0.001) level of mental well-being than nursing students in Northern Ireland. There are some areas that demand special attention by nurse educators to support the mental well-being of students and the impact of this on their education. Further research needs to be undertaken to find out how to improve students' mental well-being and identify factors that are influencing mental well-being of nursing students.