This study evaluates the effect of a self-monitoring intervention on taste alterations in breast cancer patients undergoing outpatient chemotherapy. Methods: The study was a randomized controlled trial. Thirty-four participants were divided into two groups: a self-monitoring (SMG) group (n = 17) and a control group (CG) (n = 17). A conceptual framework was developed with reference to the components of self-management, cognitive behavioral therapy, and the concepts of self-monitoring. Interventions were based on this framework. SMGs recorded their taste symptoms as homework and worked with the researcher to set goals and provide feedback four times every three weeks. In the feedback, the researcher actively listened to the SMG about their feelings and coping strategies during the taste changes, and gave approval and praise for these. The implementation period was 9 weeks for each participant; the CG was provided with conventional nursing support. The intervention was evaluated by comparing the items of symptom improvement, quality of life (QOL), and self-efficacy between the groups before and after the start of the intervention using a scale score. Scale scores were also compared for recognition of taste changes, concerns during treatment, distress, and impacts on each treatment day. Results: SMG had significantly lower scores than CG for perceived change in taste (p = 0.009), and there was an interaction with CG (p = 0.008). SMG had also significantly lower scores than CG in concern during treatment (p = 0.015). Conclusion:This study showed that a self-monitoring intervention reduced negative cognition of taste alterations and reduced discomfort. The results suggest that the self-monitoring intervention is effective nursing support for chemotherapy-induced taste alterations.