Objective To study the effect of sand storm on the activity of saliva lysozyme of middle school students and pupils.Methods 452 subjects aged 8-17 years,living in the areas where the sand storm happened frequently and infrequently,were selected with the stratified sampling and cluster sampling methods in May 2007.The activity of saliva lysozyme in saliva was measured by turbidimetric method.Results Compared with the areas where the sand storm happened frequently,in the infrequent areas,the activity of lysozyme of the boys in 12,14,16 ～17 age groups and of the girls in 12 and 14 age groups significantly decreased(P﹤0.05 or P﹤0.01).The activity of saliva lysozyme of the areas where the sand storm happened frequently was concerned with gender,age,time of daily outdoor activity during the sand storm.Conclusion Sand storm can cause the activity of saliva lysozyme decrease in the middle school students and pupils.