The purpose of this study is to explore the relationship between job stress and teaching effectiveness of primary school teacher. The researcher used questionnaire survey method in this study among teachers of the public elementary schools in Taiwan as participants. The survey tool is self-designed a questionnaire “the Relationship between Job Stress and Teaching Effectiveness of Primary School Teacher”. There are 1500 pieces of the questionnaire which were sent to229 sample primary schools in Taiwan and 849 returned copies were effective. The returned rate reached 56.6%. The data were analyzed with the methods of Mean, Standard Deviation, T-test, One-way ANOVA, Pearson Product Correlation method for statistical analysis. The results are as follow: 1. The level of job stress of primary school teachers is lower degree of average.Among them, the highest level of the job stress options is“workload”. 2. Primary school teacher’s teaching effectiveness was rated a fair performance,and the best part is“ to create learning environment”. 3. There are significant differences in job stress of primary school teachers on the part of the background variables. 4. There are significant differences in teaching effectiveness of primary school teachers on the part of the background variables. 5. There is a negative correlation between job stress and teaching effectiveness of primary school teacher. Finally, the research provided suggestions for the education administrative authorities, school administrators and primary school teachers in future researches.