(1) Background: Nurses can find people with advanced diseases or in their last days of life during their professional careers and in many different care settings. For this reason, they need to have at least a basic level of palliative care education since they are the professional cohort treating these patients in a very close way. This research aims to determine the level of knowledge in palliative care of Spanish nurses and establish any possible difference based on their experience and training in palliative care. (2) Methods: A cross-sectional design using survey methods (distributed an online questionnaire) aimed at Spanish registered nurses. A validated questionnaire (PCQN-SV) was used to determine the level of knowledge in palliative care; information on some variables to characterize the population was also collected (experience and education in palliative care, years of professional experience, academic level, and others). Uni and bivariate descriptive analyses were performed. A binary logistic regression model was also developed to identify those variables that influenced obtaining results higher than the population's average. (3) Results: Spanish nurses have a medium-low level of knowledge in palliative care, higher in those who have previous experience or education in this area. Statistically significant differences were also found according to the area in which their caring activity was developed. (4) Conclusions: It is necessary to implement strategies for the basic training of nursing professionals in palliative care to offer quality care to people in advanced stages of illnesses or at the end of their lives.