Background: Implementing evidence-based healthcare (EBHC) to improve the quality of patient care is a key issue for physicians and nurses. One of the most effective activities for achieving this is the annual topic-oriented clinical application national competition in Taiwan. Hundreds of clinical issues have been presented in this competition. By using the decomposed theory of planned behaviour (DTPB), this study explored physicians’ and nurses’ behaviour and adherence to the clinical application of EBHC after participating in the competitions. Methods: We conducted a 3-month cross-sectional online survey using a structured questionnaire adapted from the original study of the DTPB to collect behavioural and intention-related data. We also used a model of seven action stages (from aware of to adhered to) to assess target behaviours. We targeted contestants of the EBHC competitions between 1999 and 2017 as study participants. Of 631 teams, 321 teams completed the questionnaire, representing a 49.5% response rate. We applied structural equation modelling to test model fit. Moreover, we executed multivariate logistic regression to identify potential predictors. Results: Of the respondents, 33.3% reportedly reached the final adhered to stage. The DTPB model exhibited a good fit to the observed data. All constructs (usefulness, compatibility, peer influence, superior influence, self-efficacy, resource facilitating conditions, attitude, subjective norms, behavioural control, and intentions) were positively associated with the target behaviours, except for ease of use and technology facilitating conditions. Furthermore, the study model explained the variance in the target behaviours (37.0%). Having managerial duties (odds ratio [OR] =2.03, 95% confidence interval [CI] =1.10–3.77), resource facilitating conditions (OR = 1.06, 95% CI = 1.01–1.11), behavioural control (OR = 2.21, 95% CI = 1.47–3.32), and intentions (OR = 1.96, 95% CI = 1.40–2.73) were significant predictors of the achievement of the adhered to stage. Conclusions: The study demonstrated the association between determinants of behaviour and clinical applications and factors influencing adherence to EBHC among competition participants. The adherence rate was not high after the competitions, and this may be improved by promoting certain factors associated with the target behaviours.