Abstract: Objective To test the reliability and validity of a mental work load assessment scale-National Aeronautic and Space Adm inistration Task Load Index (NASA-TLX) among primary and middle school teachers.Methods Totally 1 285 primary and middle school teachers in Jiangxi province were sampled with randomized cluster sampling.The spli-thalf reliability,Cronbach's a lpha coefficient,theta coefficient,omega coefficient and correlation coefficients between item score and total score were adopted to test the reliability.The test of validity included the assessment of structure validity and discrmi inant validity.Results The split-half reliability of NASA-TLX was 0.808.Its Cronbach's alpha coefficient,the tacoef-ficient and omega coefficient was 0.758,0.782,and 0.875,respectively.The correlation coefficients between its items score and total score were allmore than 0.50(P < 0.001,except the item of performance).These results suggested that the scale had good inner consistency.The results of factor analysis showed that NASA-TLX had good structure validity.The items of NASA-TLX had good discrmi inant validity enough to distinguish different level of mental work load among prmiary and middle school teachers(P < 0.05).Conclusion NASA-TLX has good reliability and validity and could be used as a valid tool to assessmental work load of primary and middle school teachers in China after being revised properly.