This paper quantitatively compares the effects of natural disasters and social violence events would have on stock prices． Two natural disasters and two social violence event are selected as samples: Sichuan “5． 12”earthquake; Qinghai“4． 14”earthquake; Tibet“3． 14”incident; and Xinjiang“7． 5”incident． The results indicate: 1，both natural disasters and social violence event have significant negative impacts on stock prices of the listed companies where the events took place，among which“3.14”incident had the most significant effects in the short run while“5.12”earthquake had the most significant effects in the long run; 2，the impacts of two earthquakes on the prices lasted for 19 days and 8 days respectively and those of the two social violence event lasted for 7 days and 6 days—respectively natural disasters have longer impacts on stock prices than social violence event do; 3，the two earthquakes brought about 30% value losses to the stock market，Tibet“3.14”incident brought about 15% losses while the“7.5”incident brought no value losses; 4，shocks on stock prices had contagious effects．The prices of the affected stocks and their matching stocks went up and down synchronously and investors tended to chase the trends by selling low and buying high Besides，some other interesting results are drawn from our empirical study e.g．when similar events took place for the second time，the investors showed their learning ability; and no matter in natural disasters or social violence event，nationalism was observed in stock markets where both incidents were not welcomed by investors．