Purpose: to examine how evidence about the therapeutic alliance gleaned from participatory action project affected the level of this alliance and the degree of empathy of psychiatric nurses. Design and methods: quasi-experimental study in two psychiatric units. In one group, evidence-based practices that affected the therapeutic alliance were implemented; in the comparison group, there was no such intervention. Findings: the nurses from the intervention group improved their degree of empathy and factors such as agreement on objectives and tasks with the patient. Practice implications: the results confirm the possibility of measuring and improving the therapeutic relationship in psychiatric care.