When the ultrasound of 42 kHz was irradiated on a neutral mixture of 2'-deoxycytidine, 2'-deoxyguanosine, 2'-deoxythymidine, and 2'-deoxyadenosine, concentrations of all the nucleosides decreased. Addition of NaCl to the system had no effect. NaBr suppressed the reactions for all the nucleosides, but the efficiency of 2'-deoxyguanosine was low. NaI suppressed the reactions for all the nucleosides more effectively. A comparison with the results of the effects of halides on the reaction of nucleosides by a Fenton system suggested that only half of the nucleoside damage in the ultrasound-irradiated solution was caused by hydroxyl radicals formed from water by the sonication.