This study examined the Root Cause Analysis (RCA) teaching strategy on pre-service primary science teachers and instinct pre-service teachers to apply RCA teaching strategy to science curriculums. RCA Teaching Strategy is to coordinates 5 Why Method and Fishbone Diagram. The participants included 18 pre-service primary science teachers and the training courses for 4 hours a week and lasted for 18 weeks. The result shows that pre-service primary science teachers are gradually familiar with RCA teaching strategy and can apply it to science curriculums from microteaching classroom observation and teaching-portfolios. For example, in "The Influence of Heat on Materials" unit, the fifth grade students observed the balloon on the PET bottle soaked in water swelled. Students would brainstorm all causes of balloon swelled with 5-W method, and draw fishbone diagram together. Finally, they found the root cause with Root Cause Analysis. (Contains 1 figure and 3 tables.)