Abstract: Rice blast, Caused by pyricularia oryzae,is one of the main diseases in northern moun-tain area in Fujian.In the past 12 years,the evolution in prevalence of physiological races have been monitored and the results clearly indicated that the races of blast fungus is rather variable in their stability and adaptability.The variability is closely correlated with the extension period and grow-ing density of popularized rice varieties.These results possess an important significance to screen resistant parent materials, breed resistant varieties, arrange and renew varieties,forcast and pro-tect rice plants from blast diseases.