Nurses working at nursing homes are one of the most vulnerable populations for suffering burnout and compassion fatigue. In Spain, the concept of compassion fatigue and psychological flexibility related to stress in geriatric nurses has not been fully explored until now. It is important to analyze their situation in order to design robust coping and management strategies. The aim was to analyze the relationship between burnout, compassion fatigue and psychological flexibility in geriatric nurses in Spain. Participants included 291 nurses from 97 centers in 51 cities across Spain. Psychological flexibility (AAQ-II), burnout (MBI) and compassion fatigue (ProQOL) were evaluated. Responses were recievced from 281 nurses (91% women), with an average of 7.6 years of work experience. The MBI results were average (26.71), and the ProQOL scores were average for compassion fatigue (40.2%) and high for compassion satisfaction (70.3%), whereas for AAQ-II, the mean score was 37.34 (SD 4.21). The correlation was significant and negative for flexibility, burnout and compassion fatigue, and positive for compassion satisfaction. The ANOVA indicated a significant association between all variables (p < 0.05). We can conclude that geriatric nurses suffer from medium levels of burnout and compassion fatigue, together with high levels of psychological flexibility, which appears to act as a stress reliever, supporting compassion satisfaction.