This study measured changes in healthcare professionals' (HCPs) performance in tobacco cessation intervention before and 6 months after a health system intervention. The intervention involved exposure to online training for staff and the implementation of a structured organizational change-level practice model that included some strategies, comprising establishing tobacco cessation steering groups with champions in each hospital, developing tailored protocols and guidelines within each organization, conducting on-site workshops for clinicians, and creating posters and pocket materials summarizing the intervention. Pre-post evaluation in four hospitals in Barcelona province (Catalonia, Spain). We assessed the knowledge, attitudes, behaviors, and organizational factors (KABO) and the performance of each of the components of the 5As Model for Treating Tobacco Use according to a scale from 0 ("Never") to 10 ("Always") among HCPs. We performed Wilcoxon signed-rank tests for paired samples and assessed changes in performance by performing linear regression. A total of 255 HCPs completed the pre-post evaluation. All components of the 5As Model increased, with "Assist" and "Arrange a follow-up" showing the greatest improvement. Several KABO dimensions significantly increased, including individual skills (mean score: 3.3-5.7, P < .001), attitudes and beliefs (4.8-5.4, P < .001), individual commitment (5.9-6.6, P < .001), and perception of having positive organizational support (4.3-4.7, P < .001). An increase in each point in individual skills and support of the organization was associated with increased rates of 5As delivery, with the greatest associations found for "Assist" (0.60 and 0.17, respectively) and "Arrange a follow-up" (0.71 and 0.18, respectively). The intervention was successful in increasing HCPs individual skills, attitudes and beliefs, individual commitment, and perception of having positive organizational support and the performance of all components of the 5As. Future research should focus on strategies that promote organizational support, a dimension that is essential to increasing Assist and Arrange, which were less implemented at baseline.