Objective: To improve nursing practice guideline for patients with acute STEMI at Mukdahan Hospital and to evaluate the effectiveness of the practice guideline. Study Design: The action research was conducted from January 2013 to June 2014. The study has been divided into three phases: Phase 1 was patient’s characteristic study, Phase 2 was development process of practices guideline, Phase 3 was the effectiveness evaluation of the practice guideline. The sample was specifically selected for sample size of 30 and there were 73 nurses participated in this study. Research instrument was validated by experts for content validation (p = 0.88). Descriptive statistics using percentage mean, standard deviation, and inferential statistics were Chi Square test, Fisher’s Exact Test and Independent t-test.