Humanization of nursing is related to certain social and moral variables. Moral sensitivity, empathy, and prosocial behavior help understand a situation and make decisions that benefit the patient. The objective of this study is to find out how these variables are related, and define the differences in moral sensitivity, empathy, and prosocial behavior in humanization of nursing. We also analyzed the mediating role of empathy in the relationship between moral sensitivity and prosocial behavior. The sample was made up of 330 Spanish nurses aged 22 to 56, who completed the HUMAS Scale and adapted versions of the Basic Empathy Scale, the Moral Sensitivity Questionnaire, and the Prosocial Behavior Scale. Descriptive analyses, bivariate correlations and multiple mediation models were calculated. The results found significantly different mean scores between all the groups in responsibility and moral strength, cognitive empathy, and prosocial behavior, and in moral burden, the differences were in the high-humanization-score group compared to the low-score group. Furthermore, the mediation models showed the mediating effect of cognitive empathy between the responsibility, strength, and moral burden factors on prosocial behavior, but not of affective empathy. The study concluded that humanization in nursing is closely related to moral sensitivity, cognitive empathy, and prosocial behavior. This facilitates a helping, caring, and understanding attitude toward patient needs, but without the affective flooding that affective empathy can lead to.