BACKGROUND: Virtual reality (VR) is a novel technology which provides a great opportunity to reduce some of the adverse effects of chemotherapy. OBJECTIVE: Our study aims to investigate the effects of VR on the emotional states of paediatric oncology patients (n = 29, age: 10-18 years) receiving chemotherapy in a clinical setting with a crossover design. METHODS: Children played a VR game in the experimental, and a mobile game in the control condition. Psychological (happiness, joy, fear, nervousness, anxiety, alertness, patience) and physiological variables (heart rate, systolic blood pressure, electrodermal activity), as well as pain and nausea were measured before and after the sessions. Data were analysed with multiple 2-way repeated measures ANOVA. RESULTS: Joy ( = .003) and happiness ( < .001) increased significantly when using VR, while there was no change in the control condition. Anxiety decreased ( = .002) and patience increased ( = .015) in both conditions, implying no additional benefit of VR. Children were more fearful before the VR session ( = .005), which disappeared after it. In case of physiological parameters, electrodermal activity decreased ( = .01) significantly after playing the mobile game, but not after the VR one. CONCLUSIONS: Our investigation point to the positive effects of VR on mood in paediatric oncology inpatients, thus, it could be used as a new tool in improving patients' well-being during chemotherapeutical treatment. Our results indicate that VR is an effective tool in improving patients' well-being during chemotherapeutic treatment.