Background: Kidney transplant failures are caused primarily by lack of adherence to immunosuppressivemedication regimens by patients after transplantation. A number of studies have indicated that health-related beliefs are an effective predictor of health-related behavior. Purpose: The aim of this study is to understand the influence of the personal characteristics and health-related beliefs of patients on adherence to treatment with immunosuppressive medication based on the Health Belief Model. Methods: This cross-sectional study distributed questionnaires to patients who had been recruited via purposive sampling at one medical center in Taipei. All of the potential participants had undergone kidney transplantation at least 6 months previously. The self-developed questionnaire collected data in three areas: personal characteristics, health-related beliefs regarding transplant rejection, and adherence to the immunosuppressive medication regimen. One hundred twenty-two valid questionnaires were received. The collected data were analyzed using descriptive statistics, independent t test, one-way analysis of variance, Pearson’s correlation, and multiple regression. Results: Participants who had received dialysis treatment or had experienced rejection perceived susceptibility to rejection more strongly than those who had not. Participants who had undergone transplantation in Taiwan, had experienced more drug-related symptoms, or had contracted severe to extremely severe infections in the past showed lower rates of adherence to treatment with immunosuppressive medication. Adherence to medication regimens correlated negatively with length of time since transplantation. Length of time since transplantation, drug-related symptoms, perceived susceptibility to rejection, and perceived benefits of treatment were identified as major predictors of adherence to immunosuppressive medication regimens. Conclusions: The results partially conformed to the concepts of the Health Belief Model. Perceived susceptibility to rejection and perceived benefits of adherence to treatment were found to predict adherence rates. Patient education should be enhanced to reduce the risks of rejection and increase adherence rates to improve outcomes.